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Frontispiece. 


New  Half,  Old  Half, 

Veneer  Construction.  Solid  Masonry 

Walls. 

THE  MONADNOCK  BUILDING. 


ARCHITECTURAL  ENGINEERING. 


WITH  SPECIAL  REFERENCE  TO 

HIGH  BUILDING  CONSTRUCTION, 

INCLUDING  MANY  EXAMPLES  OF 

CHICAGO  OFFICE  BUILDINGS. 


BY 

JOSEPH  KENDALL  FREITAG,  B.S.,  C.E. 


FIRST  EDITION. 
FIRST  THOUSAND. 


NEW  YORK: 
JOHN  WILEY  &  SONS. 
London:  CHAPMAN  &  HALL,  Limited. 
1895. 


Copyright,  1895, 

BY 

JOSEPH  K.  FREITAG. 


ROBERT  DRUMMOND,  ELECTROTYPER  AND  PRINTER,  NEW  YORK. 


THE  GETTY  CENTER 
LIBRARY 


PREFACE. 


The  author  has  attempted,  in  the  following-  pages,  to 
define  and  illustrate,  in  a  manner  as  practicable  as  possible, 
such  of  the  fundamental  principles  in  the  design  of  the 
modern  high  building  as  may  prove  useful  to  architects 
and  engineers  alike. 

While  the  technical  press  of  the  country  has  devoted 
considerable  attention  to  many  of  the  individual  subjects 
here  considered,  yet  the  realization  of  a  want  of  collective 
data  on  the  subject  of  Architectural  Engineering  has 
induced  the  writer  to  present  this  volume. 

As  more  and  more  of  the  principles  of  construction  are 
being  added  to  the  curricula  of  our  architectural  schools, 
and  as  many  of  our  engineering  students  are  adopting 
building-  construction  as  a  specialty,  it  is  hoped  that  this 
effort  will  serve  to  unite  still  more  closely  the  work  of  the 
one  with  that  of  the  other. 

The  author  would  mention  the  efforts  of  one  highly 
esteemed  and  dearly  beloved  in  the  engineering  profession, 
Mr.  E.  L.  Corthell,  who  has  been  striving  for  several  years 
to  see  the  two  professions  united  by  establishing  an  Inter- 
national Institute  of  Engineers  and  Architects,  as  well  as  a 
technical  School  of  Architecture  and  Engineering  at  the 
new  University  of  Chicago.  The  writer  would  also 
acknowledge  the  warm  interest  displayed  in  this  work  by 
his  former  professor  of  engineering,  Prof.  C.  E.  Greene,  of 
the  University  of  Michigan. 

iii 


iv 


PRE  FA  CE. 


The  following  chapters  are  arranged  in  the  order  in 
which  the  calculations  for  such  structural  work  must  pro- 
ceed, starting  with  the  load-bearing  floor  system,  thence 
through  the  successive  stages  to  the  foundations.  The 
latter  would  seem  to  require  the  first  attention  ;  but  as  they 
are  the  last  to  be  calculated,  being  dependent  on  all  other 
considerations,  they  have  here  been  placed  last.  The  illus- 
trations and  examples  given  have  been  largely  obtained 
through  the  courtesy  of  the  architects  of  the  respective 
buildings.  An  endeavor  has  been  made  to  present  only  the 
most  practical  methods. 

Joseph  Kendall  Freitag. 

Chicago,  May,  1895. 


CONTENTS. 


CHAPTER  I. 

PAGE 


Introductory   i 

CHAPTER  II. 

Fire  Protection   9 

CHAPTER  III.' 

Skeleton  Construction— Examples— Erection,  etc   24 

CHAPTER  IV. 

Floors  and  Floor  Framing   54 

CHAPTER  V. 

Exterior  Walls— Piers   88 

CHAPTER  VI. 

Spandrels  and  Spandrel  Sections — Bay  Windows   100 

CHAPTER  VII. 

Columns   113 

CHAPTER  VIII. 

Wind  Bracing...   136 


CHAPTER  IX. 

Pari  itions— Roofs— Miscellaneous   163 

CHAPTER  X. 

Foundations   171 

CHAPTER  XI. 

Unit-strains— Specifications   201 

CHAPTER  XII. 

Building  Laws   216 


LIST  OF  ILLUSTRATIONS. 


FIG.  PAGE 

1.  Re/iance  Building,  Chicago   17 

2.  Arrangement  for  Pipe-space  in  Halls   22 

3.  Chicago  Stock  Exchange  Building.    Perspective   25 

4.  Chicago  Stock  Exchange  Building.    Basement  Plan   27 

5.  Chicago  Stock  Exchange  Building.    Ground  Floor  Plan   28 

6.  Chicago  Stock  Exchange  Building.    Typical  Office  Floor  Plan.  29 

7.  Marquette  Building,  Chicago.    Perspective   30 

8.  Marquette  Building,  Chicago.    Typical  Office  Floor  Plan. . ... .  31 

9.  Reliance  Building.    Typical  Office  Floor  Plan   32 

10.  Masonic  Temple,  Chicago   34 

11.  New  York  Life  Insurance  Building.    Perspective   35 

12.  New  York  Life  Insurance  Building.    Plan  of  Banking  Floor...  36 

13.  New  York  Life   Insurance  Building.     Typical   Office  Floor 

Plan  *   37 

14.  Fort  Dearborn  Building.    Perspective   38 

15.  Fort  Dearborn  Building.    Typical  Office  Floor  Plan   40 

16.  Champlain  Building.    Typical  Office  Floor  Plan   41 

17.  Old  Colony  Building.    Perspective   42 

18.  Typical  Framing  Plan  of  Fort  Dearborn  Building   43 

19.  Typical  Framing  Plan  of  Reliance  Building   44 

20.  Reliance  Building  during  Construction   48 

21.  Reliance  Building  during  Construction   49 

22.  Brick  Arch  Construction   55 

23.  Corrugated  Iron  Arch   55 

24.  Tile  Arch  used  in  Equitable  Building,  Chicago  (1872)   55 

25.  Tile  Arch  used  in  Montauk  Building,  Chicago  (1881).   56 

26.  Tile  Arch  used  in  Home  Insurance  Building,  Chicago  (1884).  . .  56 

27.  Arch  showing  Tile  Filling  Blocks  used  in  Woman's  Temple, 

Chicago.   57 

vii 


viii  LIST  OF  ILLUSTRATIONS. 

FIG  PAGE 

28.  Panelled  Beam,  Fire-proofed  0   58 

29.  Fire-proofed  Girder   58 

30.  The  Lee  Flat  Arch   59 

31.  The  Johnson  Type  of  Flat  Arch  . .   61 

32.  The  Austria  Tile  Arch   65 

33.  The  Melan  Arch,  Short  Span   67 

34.  The  Melan  Arch,  Long  Span   67 

35.  Arch  of  Metal  Straps  and  Concrete   69 

36.  Arch  of  Wire  and  Concrete,  Panelled  Soffit    69 

37.  Arch  of  Wire  and  Concrete,  Flush  Soffit   70 

38.  Elliptical  Concrete  Arch   71 

39.  Segmental  Tile  Arch   72 

40.  Segmental  Tile  Arch  used  in  Sibley  Warehouse,  Chicago   72 

41.  Standard  Connection-angles   85 

42.  Standard  Connection-angles  :   86 

43.  Isometrical  View  of  Connection  of  Floor-beam  to  Girder   87 

44.  Detail  of  Terra-cotta  Front.    Reliance  Building   93 

45.  Section  through  Wall  at  Main  Entrance  to  Masonic  Temple...  94 

46.  Detail  of  Corner  Pier  for  Reliance  Building   97 

47.  Detail  of  Wall  Girders  in  Reliance  Building   98 

48.  Diagram  of  Thickness  of  Walls  for  Buildings  Devoted  to  Sale 

and  Storage  of  Merchandise   99 

49.  Diagram  of  Thickness  of  Walls  for  Hotels  and  Office  Buildings 

other  than  Skeleton  Construction   99 

50.  Diagram  of  Thickness  of  Walls  for  Office  Buildings  carrying 

Wall  Weight  only   99 

51.  Spandrel  Section.    Ashland  Block   101 

52.  Spandrel  Section.    Reliance  Building   101 

53.  Connection  of  Cast  Mullions.    Reliance  Building   101 

54.  Spandrel  Section,  nth  floor.    Fort  Dearborn  Building   102 

55.  Spandrel  Section,  12th  floor.    Fort  Dearborn  Building   103 

56.  Spandrel  Section,  1st  floor.    Fort  Dearborn  Building   103 

57.  Spandrel  Section,  Roof  and  Cornice.    Fort  Dearborn  Building.  104 

58.  Spandrel  Section.    Marquette  Building   105 

59.  Spandrel  Section.    Marshall  Field  Building   106 

60.  Spandrel  Section.    Marshall  Field  Building   106 

61.  Spandrel  Section  through  Court  Wall  of  Marshall  Field  Building  107 

62.  Spandrel  Section  through  Typical  Court  Wall..   108 


LIST  OF  IL L  US TRA  T10NS.  i X 

FIG.  PAGE 

63.  Spandrel  Section  through  Bay  Window.    Masonic  Temple   109 

64.  Spandrel  Section  at  Bottom  of  Bay  Window.    Masonic  Temple.  109 

65.  Half  Plan  of  Metal-work  in  Bay  Window.    Reliance  Building. .  no 

66.  Half  Plan  through  Bay-window  Walls.    Reliance  Building  ....  no 

67.  Spandrel  Section  through  Centre  of  Bay.    Reliance  Building..  111 

68.  Spandrel  Section  at  Side  of  Bay.    Reliance  Building   111 

69.  Floor  and  Ceiling  Supports  in  Bay  WTindow.    Reliance  Building  112 

70.  Details  of  Joints  for  Cast  Columns   114 

71.  Detail  of  Larimer  Column   122 

72.  Detail  of  Larimer  Column   122 

73.  Detail  of  Gray  Column  and  Connecting  Girders   125 

74.  Detail  of  Phcenix  Column    125 

75.  Detail  of  Z-bar  Column.    Monadnock  Building   127 

76.  Detail  of  Phcenix  Column   128 

77.  Detail  of  Phcenix  Column  used  in  Old  Colony  Building   129 

78.  Detail  of  Box  Column   129 

79.  Section  of  Z-bar  Column  used  in  "  The  Fair  "  Building   130 

80.  Method  of  Fire-proofing  Phcenix  Column   134 

81.  Method  of  Fire-proofing  Box  Column   134 

82.  Method  of  Fire-proofing  Z-bar  Column   134 

83.  Method  of  Fire-proofing  Columns  in  Monadnock  Building   134 

84.  Diagram  of  Wind  Bracing  by  means  of  Sway-rods   139 

85.  Diagram  of  Wind  Bracing  by  means  of  Sway-rods   139 

86.  Diagram  of  Wind  Bracing  by  means  of  Portals   139 

87.  Diagram  of  Wind  Bracing  by  means  of  Knee-braces   139 

88.  Figure  showing  Analysis  of  Sway-rod  Bracing   141 

89.  Figure  showing  Typical  Sway-rod  Bracing   143 

90.  Wind  Bracing  used  in  Masonic  Temple   144 

91.  Floor  Plan  of  Venetian  Building   144 

92.  Wind  Bracing  in  Venetian  Building   145 

93.  Detail  of  Channel-struts.    Venetian  Building   146 

94.  Detail  of  Cast  Blocks.    Venetian  Building   146 

95.  Partial  Cross-section  of  Venetian  Building    147 

96.  Figure  showing  Analysis  of  Portal  Bracing   149 

97.  Portal-strut  used  in  Monadnock  Building   151 

98.  Cross-section  showing  Portals  in  Old  Colony  Building   151 

99.  Detail  of  Portal  in  Old  Colony  Building   152 

100.  Figure  showing  Analysis  of  Knee-bracing   153 


X  LIST  OF  ILLUSTRATIONS. 

FIG.  PAGE 

101.  Detail  of  Knee-bracing  used  in  Isabella  Building   154 

102.  Channel-struts  and  Gussets  used  in  Exterior  Walls  of  Fort 

Dearborn  Building   155 

103.  Detail  of  Column  Joint  in  Pabst  Building,  Milwaukee   158 

104.  Detail  of  Column  Splice  in  Reliance  Building   159 

105.  Detail  of  Book  Tile   164 

106.  Hall  and  Main  Entrance  to  Marquette  Building   166 

107.  Hall   and    Main   Entrance   to   New   York    Life  Insurance 

Building   167 

108.  Hall  and  Main  Entrance  to  Fort  Dearborn  Building   168 

109.  Rail  Footing   174 

no.  Masonry  Footing   174 

in.  Beam  and  Rail  Footing   181 

112.  Beam  Footing  used  in  Marquette  Building   184 

113.  Double  Footing  used  in  Marquette  Building   184 

114.  Plan  of  Cantilever  Footing   186 

115.  Elevation  of  Cantilever  Footing   186 

116.  Line  of  Flexure  for  Continuous  Girder   187 

117.  Figure  showing  Analysis  of  Cantilever  Footing   187 

118.  Figure  showing  Analysis  of  Continuous  Girder   189 

119.  Plan  of  Foundations.     Manhattan  Life  Insurance  Building, 

New  York   199 

120.  Cross-section  showing  Foundations  of  Manhattan  Life  Insur- 

ance Building,  New  York  ,   200 


ARCHITECTURAL  ENGINEERING. 


CHAPTER  I. 

INTRODUCTORY. 

Among  the  most  noteworthy  examples  of  Architectural 
Engineering  in  recent  years,  "  Le  Tour  Eifel  "  stands  unique 
— a  most  perfect  expression  of  this  recently  coined  term, 
signifying  a  complete  union  of  the  great  art  of  architecture 
and  the  science  of  engineering.  While  universally  accepted 
as  distinctly  an  engineering  feat,  this  tower  possesses  such 
perfect  structural  beauty  that  it  may  well  lay  claim  to  the 
eulogies  of  architectural  critics — eulogies  that  should  be  all 
the  more  emphatic  when  we  stop  to  consider  how  few  and 
far  between,  in  modern  times,  are  the  creations  of  the  engi- 
neer that  can,  at  the  same  time,  appeal  to  the  architectural 
artist  or  designer,  as  embodying  the  beauty  of  form  with 
the  excellence  of  construction  ;  while  the  reverse  may  truly 
be  said  of  modern  architecture.  For  who  may  claim  justly 
that  our  present  architectural  efforts  are  true,  characteristic 
expressions  of  modern  life,  or  reflections  of  the  progress 
that  has  characterized  our  age — as  classical  architecture 
embodied  classical  life  and  mediaeval  architecture  expressed 
mediaevalism  ? 

The  science  of  engineering  has,  at  least,  been  progress- 
ive, keeping  pace  with  modern  developments,  while  archi- 
tecture, for  the  most  part,  has  been  stationary,  content  to 


2 


A  R CHI TE  C T  URA  L  ENGINEERING. 


copy  the  original  form  of  a  civilization  whose  substance 
has  undergone  ages  of  evolution.  Hence  arise  the  causes 
for  the  present  antagonism  in  these  two  closely  related  pro- 
fessions. There  should  be  none,  but  that  there  is,  no  one 
will  deny.  One  of  the  most  prominent  engineers  of  the 
United  States  has  been  heard  to  characterize  architects  as 
"  milliners,"  and  their  work  as  "  millinery  "  or  "  gingerbread 
decoration  ";  while  the  architect,  on  his  own  little  pedestal  of 
pure  art,  scorns  the  engineer  as  incapable  of  producing  the 
beautiful.  There  is,  doubtless,  partial  justice  in  each  of 
these  criticisms;  the  architect's  blind  devotion  to  classic 
forms  becoming  as  much  of  a  hindrance  to  the  practical 
aims  of  the  engineer,  as  the  barren  stamp  of  utility,  glaring 
from  a  purely  engineering  work,  is  an  offence  to  the  eye  of 
the  artistic  designer.  But  the  keynote  has  already  been 
sounded  for  a  more  perfect  union  between  these  two  pro- 
fessions, each  of  which  is  the  necessary  complement  of  the 
other. 

Although  the  term  architectural  engineering  has  but 
recently  sprung  into  use,  the  perfect  union  of  the  two  arts 
is  as  old  as  the  arts  themselves.  Pyramids,  obelisks, 
temples,  palaces,  and  sepulchres,  all  show  that  the  architects 
of  early  days  were  the  engineers  as  well.  Vitruvius,  the 
only  ancient  whose  ideas  on  architecture  have  been  pre- 
served for  us,  established  three  qualities  as  indispensable 
in  a  perfect  building  :  stability,  utility,  and  beauty, — the  first 
two  of  which  certainly  lie  within  the  range  of  the  science 
of  engineering.  As  a  proof  that  those  early  architects 
were  governed  by  the  laws  of  Vitruvius,  we  have  but  to 
look  upon  the  pyramids  of  Egypt,  the  vast  monoliths  of 
Rome,  the  temples  of  Sicily,  or  the  massive  Parthenon. 
Their  graceful  proportions  and  harmony  of  design  have 
for  centuries  made  of  the  architect  an  admiring  copyist, 
while  their  massiveness  and  stability  suggest  to  the  en- 


/ 


IN  TR  OD  UCTOR  Y.  3 

gineer  the  possibilities  of  human  power.  Take  tor  example 
one  of  the  largest  pyramids  not  far  from  the  city  of  Cairo. 
This  rough,  awe-inspiring  mass  of  masonry  covers  u  acres 
of  the  sands  of  the  Nile,  while  its  height  is  but  little  less 
than  our  Washington  Monument,  or  nearly  500  feet. 
Again,  consider  the  temple  of  Babylon,  660  feet  in  height, 
built  of  blocks  of  stone  20  feet  long,  used  in  a  brick-like 
fashion,  some  of  them  being  15  feet  broad  and  7  feet  thick  ; 
or  the  massive  remains  of  an  Egyptian  temple,  the  walls 
of  which  were  found  to  be  24  feet  thick;  while  at  the  gates 
of  Thebes  the  foundation  walls  were  50  feet  thick  and  per- 
fectly solid. 

The  ethnologist  tells  of  an  age  of  clay,  then  stone  in 
the  rough  and,  later,  polished  ;  an  age  of  bronze,  then  iron  ; 
and  now  we  add  steel  and  the  newer  materials.  Architec- 
ture, as  represented  in  the  temples,  tombs,  palaces,  and 
habitations  of  man,  has  always  been,  like  literature,  the 
surest  indication  of  the  customs,  arts,  and  needs  of  the 
people  who  produced  it — in  fact,  a  perfect  reflection  of  the 
civilization  in  which  it  is  found.  "  Cain,  the  son  of  Adam, 
builded  a  city," — the  rude  mud  hut  or  the  flimsy  structure 
of  reeds  serving  as  man's  habitation  in  primitive  times,  imi- 
tating the  nests  of  birds,  of  which  modifications  still  exist 
in  China  and  other  Eastern  countries,  as  well  as  in  many 
parts  of  dark  Africa.  The  later  days  of  clay  and  straw  and 
then  burned  brick  were  succeeded  by  the  age  of  stone, 
reaching  such  a  height  of  excellence  in  the  works  of  the 
Greeks  and  Romans,  and  the  castles  and  cathedrals  of  the 
middle  ages.  The  temple  of  Solomon,  rebuilt  by  Herod 
at  Jerusalem,  was,  so  the  Bible  states,  46  years  in  erection, 
with  stones  46  feet  long,  21  feet  high,  and  14  feet  thick, 
while  some  were  of  the  great  length  of  82  feet.  Would  it 
not  tax  the  ingenuity  of  an  engineer  in  our  own  advanced 
age  to  handle  such  masses  of  stone  ?    Architecture  and  en- 


4 


ARCHITECTURAL  ENGINEERING. 


gineering  certainly  worked  in  harmony  in  these  examples,, 
which  must  ever  rank  with  the  greatest  creations  of  man. 

Now,  with  the  hurrying  strides  of  civilization,  comes  a 
demand  for  a  cheaper  and  quicker  construction,  a  medium 
capable  of  being  more  easily  handled  than  the  huge  blocks 
of  stone  of  early  ages;  while  the  principles  of  statics  and 
the  economics  of  construction  present  themselves  with 
ever  increasing  clamor  for  solution  and  application,  until 
we  boast  that  our  age  is  one  of  specialties,  involving  an 
exactness  hitherto  unknown  in  the  observance  of  all  the 
laws  of  nature  formulated,  as  they  are,  into  exact  sciences. 

It  was  but  natural,  in  the  examples  we  have  considered, 
that  architecture  should  go  hand  in  hand  with  engineering,, 
for  the  architect  was  the  engineer,  employing  rule  of  thumb 
methods,  to  be  sure,  and  knowing  little  of  the  laws  of 
statics  or  dynamics.  Indeed  it  was  not  till  the  thirteenth 
century  that  the  solution  of  the  theory  of  arches  and  vaults 
was  attempted.  Old,  old  indeed,  is  the  relation  of  friend- 
ship that  has  existed  between  the  naturally  allied  arts  of 
architecture  and  engineering — a  mutual  bond,  which  will, 
we  believe,  give  us  still  more  perfect  examples  of  the 
strength  and  beauty  that  architectural  engineering  makes 
possible  :  architectural,  in  reference  to  the  expression  and 
beauty  of  the  edifice — engineering  (perhaps  partially,  if  not 
wholly,  hidden  from  the  eye),  in  construction,  durability,  and 
magnitude  that  result  from  the  possibilities  which  open  up 
before  the  mind  accustomed  to  dealing  with  the  matter 
and  forces  of  nature,  and  adapting  them  to  the  ever-increas- 
ing wants  of  an  exacting  public.  The  materials  of  nature 
assume  higher  and  higher  planes  in  the  fulfilment  of  man's 
needs,  as  he  constantly  overcomes  more  of  the  natural  de- 
structive elements  and  agencies  by  applying  himself  with 
scrupulous  exactness  to  every  detail  of  work.  Considering 
the  present  tendency  to  specialization,  it  seems  absurd  to 


IN  TR  OD  UCTOR  Y.  $ 

suppose  that  the  architect  may  eventually  be  employed 
simply  as  an  ornamental  draughtsman  by  the  engineer,  or 
that  the  engineer  may  become  subservient  to  the  architect. 
Either  profession  is  too  noble  and  comprehensive  in  itself 
to  permit  of  such  absorption.  It  is  but  a  natural  prejudice 
to  give  first  importance  to  one's  own  branch  of  work  ;  and, 
indeed,  the  engineer  quite  justly  claims  a  prerogative,  since 
upon  the  accuracy  of  his  calculations  depend  the  stability 
of  the  structure  and  the  safety  of  the  tenants.  But,  on  the 
other  hand,  one  cannot  severely  censure  the  architect  for 
ridiculing  such  work  as  many  of  our  best  engineers  send 
forth,  as  devoid  of  beauty  or  even  harmony  of  line.  It  is 
apparent,  therefore,  that  the  truest  expression  of  our  life 
and  civilization  must  be  found  in  a  more  perfect  harmony 
of  these  two  professions.  The  architect  of  early  days  was 
enabled  by  rule  of  thumb  methods,  good  judgment,  and  a 
knowledge  of  past  examples  to  produce  the  structures  he 
built;  but  with  the  exactness  of  our  professional  work  at 
the  present  time,  and  the  multifold  necessities  of  our  com- 
prehensive civilization,  the  architect  who  endeavors  to 
compass  the  sphere  of  the  trained  engineer  will  find  the 
longevity  of  Methuselah  desirable  for  his  education.  Let 
the  engineer  know  more  of  art  and  appreciate  its  value,  and 
let  the  architect  know  as  much  as  possible  of  construction 
and  the  lawrs  of  the  forces  of  nature.  But  that  either  may 
fully  grasp  the  details  of  both  professions  seems  well-nigh 
impossible. 

The  architect  has  been  accustomed  to  say  that  such  a 
perfect  union  is  impracticable,  but  the  architectural  critics  of 
to-day  are  demanding  it,  as  is  shown  by  the  following  :  "  In 
art,  as  in  nature,  an  organism  is  an  assemblage  of  interde- 
pendent parts,  of  which  the  structure  is  determined  by  the 
function,  and  of  which  the  form  is  an  expression  of  the 
structure."    Again  :  "  That  form  is  pleasing  to  good  taste 


6 


ARCHITECTURAL  ENGINEERING. 


which  shows  and  reveals  its  use.  That  form  reveals  the 
use  most  successfully  whose  surface  and  outlines  and  whose 
skeleton  or  frame  speak  for  themselves,  and  are  not  ob- 
scured by  misplaced  ornament." 

If  these  quotations  from  purely  architectural  critics, 
without  reference  to  engineering,  are  to  be  given  value, 
then  surely  a  more  rational  union  of  excellent  structural 
design  on  economic  principles,  with  perfect  architectural 
expression  of  the  underlying  organism,  is  not  only  possible 
but  necessary  for  a  proper  reflection  of  our  civilization. 
The  people  of  our  country  have  demanded  "  sky-scrapers," 
in  accordance  with  the  strong  tendency  to  centralization. 
Newr  problems  have  been  created  and  new  necessities  im- 
posed, and  the  engineer  has  come  to  the  front  with  the 
steel  and  terra-cotta  of  the  "Chicago  construction,"  as  the 
means  of  solution  on  his  part ;  but  it  remains  for  the  archi- 
tect to  give  true  expression  and  permanent  form  to  what 
the  engineer  has  evolved.  It  is  from  the  union  of  the 
results  obtained  by  a  rational  division  of  labor  in  the  art  of 
building  that  we  hope  for  the  perfect  architecture  of  the 
present  age. 

It  has  been  said  that  our  civilization  has  demanded  a 
medium  of  construction  more  in  accord  with  the  push  and 
hurry  and  economy  of  our  day  than  is  found  in  the  mas- 
sive masonry  construction ;  a  substance  combining  the 
strength,  durability,  and  adaptability  required  by  the  de- 
mands of  commerce  and  rapid  progress.  In  the  architec- 
tural history  of  our  own  country  we  have  not  confined 
ourselves  to  any  one  material  long  enough  to  develop  for 
it  a  unique,  characteristic  style  of  representation.  Our 
architectural  form  has,  rather,  been  a  series  of  rapid 
changes.  The  refined  and  sober  examples  of  our  colonial 
forefathers  rapidly  gave  way  to  the  more  ostentatious 
efforts  of  the  jig-saw  in  our  frame  construction,  and  this 


INTRODUCTORY.  7 

period  of  the  shingle  and  fretwork  gave  place  to  the  rows 
of  red  brick,  and  later  the  brown-stone  front,  with  all  its 
attendant  horrors  in  galvanized  iron.  Cast  iron,  too,  has 
held  its  sway  for  its  own  little  period,  only  to  be  displaced 
by  its  more  refined  and  enduring  successor,  steel.  Our 
present  epoch  has  been  characterized  so  often  as  one  of 
steel  and  terra-cotta  that  the  subject  is  becoming  trite 
indeed  ;  but  only  through  the  combination  of  these  ma- 
terials have  the  huge  frame-works  which  now  mark  our 
large  American  cities  become  possible.  And  as  the  <4  sky- 
scraper "  office  buildings  present  interesting  problems  in 
architectural  engineering,  which  are  being  constantly  dis- 
cussed in  the  technical  press  of  to-day,  some  of  the  con- 
structional points  involved  will  be  considered  here  with 
special  reference  to  "  Chicago  construction,"  a  construction 
which  has  almost  universally  been  attributed  to  the  skill 
of  the  architect,  though  in  only  too  many  cases  the  archi- 
tect, who  has  designed,  as  it  were,  the  sugar  coat,  to  make 
the  exterior  palatable  to  the  public,  reaps  all  the  reward 
for  what  the  engineer  has  made  possible. 

The  fact  that  in  our  large  cities  it  is  found  most  advan- 
tageous as  to  time  and  convenience  for  business  transac- 
tions, to  have  our  commercial  headquarters  and  office-build- 
ing district  concentrated  within  a  limited  area,  has  caused 
the  adoption  of  buildings  numbering  from  16  to  over  20 
stories.  Increased  floor-space  must  be  obtained  to  realize 
on  the  investment,  and  it  is  evident  that  these  tower-like 
structures  must  continue  to  increase  in  numbers,  when  we 
note  the  abnormally  enhanced  prices  to  which  the  value 
of  land  is  rising.  The  American  Surety  Company  in  New 
York  City  might  be  mentioned  as  paying  the  sum  of 
$1,500,000  in  1894  for  a  piece  of  property  about  85  feet 
square,  which  would  be  at  the  rate  of  $8,000,000  per  acre. 

The  continued  development,  however,  of  this  central]- 


8 


ARCHITECTURAL  ENGINEERING. 


zation  of  business  operations  is  attended  by  many  vexing- 
difficulties,  the  attempted  solution  of  which  has  caused  a 
number  of  clauses  of  restriction  to  appear  in  the  municipal 
building  laws.  Considerable  discussion  has  been  going  on 
about  the  sanitary  aspect  of  this  question;  the  damp,  un- 
wholesome, and  microbe-laden  air  which  must  lurk  in  the 
deep  valleys  or  streets  between  mountainous  structures  on 
each  side ;  the  dark  and  uninviting  offices  of  the  lower 
stories,  which  would  soon  become  vacant ;  and  the  con- 
gested condition  of  our  sidewalks  when  our  vertical  carry- 
ing capacity  is  greater  than  our  horizontal  or  street 
capacity — all  are  considerations  of  grave  importance. 

But  that  the  proper  regulation  of  building  operations, 
with  their  attendant  difficulties  and  future  possibilities  of 
development  and  style,  may  be  successfully  accomplished 
by  general  municipal  ordinances  is  very  doubtful.  The 
building  laws  of  many  of  the  larger  cities  already  prescribe 
a  maximum  height  for  all  structures  ;  but  considering  high 
buildings,  per  se,  it  is  evident  that  it  is  not  so  much  legisla- 
tion limiting  the  possibilities  of  design  that  is  needed,  as  it 
is  laws  compelling  the  appointment  of  competent  engineers 
to  supervise  the  designs,  specifications,  and  execution  of 
large  buildings,  and  possibly  a  competent  board  of  archi- 
tects to  pass  on  the  proposed  location  of  an  extraordinarily 
high  structure.  It  would  be  well  if  we  adopted  more  of 
the  European  practice,  giving  harmonious  appearance  to 
our  thoroughfares  and  considering  the  specific  conditions 
of  each  new  structure  of  monumental  pretensions,  instead 
of  binding  all  through  an  inflexible  law.  Edifices  fronting 
on  parks  or  open  spaces  might  then  be  treated  in  more 
heroic  proportions  than  those  of  narrow  by-ways,  and  the 
incongruous  mixture  of  ups  and  downs,  side  by  side,  might 
give  place  to  some  semblance  of  harmony  between 
neighbor  and  neighbor. 


CHAPTER  II. 
FIRE  PROTECTION. 

Before  considering  the  details  of  skeleton  construction 
it  will  be  well  to  consider  the  general  subject  of  fire-proof- 
ing, with  its  effectiveness  and  its  limitation. 

The  total  fire  loss  in  the  United  States  during  the  year 
1894  was  about  $128,000,000,  of  which  the  insurance  com- 
panies paid,  as  their  share,  some  $81,000,000.  This  stupen- 
dous drain  on  the  resources  of  the  nation  ma)7  be  better 
appreciated  if  we  consider  that  the  full  value  of  the  pig 
iron  production  for  the  same  year  was  about  $75,000,000. 

When  to  this  fire  loss  we  add  the  estimated  amount 
necessary  to  maintain  the  fire  departments,  and  to  sustain 
the  fire  insurance  companies,  the  grand  total  will  exceed 
$175,000,000  annually. 

If,  then,  it  is  true,  as  stated  by  underwriters  that  forty 
per  cent  of  all  fires  are  attributable  to  causes  easily  pre- 
vented, a  proper  treatment  of  the  fire  problem  certainly  be- 
comes a  very  practical  and  economic  inquiry. 

The  subject  of  proper  fire  protection  is  now  recognized 
as  a  legitimate  and  important  branch  of  engineering.  It  is 
no  longer  confined  exclusively  to  endeavors  to  protect 
human  life,  but  is  greatly  increasing  in  scope,  demanding 
very  careful  thought  from  its  economic  standpoint  as  well. 
The  old  adage  of  an  ounce  of  prevention  being  better  than 
a  pound  of  cure  is  slowly  but  surely  demonstrating  its 
truth  as  applied  to  the  ravages  of  fire,  as  well  as  of  disease, 
and  the  specialist  who  enters  this  broad  field  of  research 
and  improvement  must  meet  causes  and  effects  with  a  pre- 

9 


10 


ARCHITECTURAL  ENGINEERING. 


cision  not  less  exact  than  does  his  medical  brother.  Con- 
flagration has  formerly  been  looked  upon  as  an  inevitable 
calamity,  inflicted  by  a  supernatural  agency ;  and  property- 
owners  have  been  content,  year  after  year,  to  pay  enormous 
insurance  rates,  suffering  with  resignation  the  destruction 
of  their  property  and  the  annihilation  of  their  business. 
Add  to  these  the  loss  of  articles  of  peculiar  associations, — 
heirlooms  and  treasures  of  art  and  science, — and  the  possi- 
bility of  relief  from  this  Damoclean  sword  of  conflagration 
is  a  liberation  indeed.  And  that  this  question  of  fire  waste 
is  being  seriously  considered  in  all  its  aspects  and  by  all 
classes  of  society  is  shown  by  the  widening  facilities  for 
the  use  of  fire-proof  construction.  The  realization  of  low 
prices  in  the  building  market  has  served  to  overthrow 
many  of  the  hitherto  unquestioned  prejudices  in  regard  to 
fire-proof  construction,  and  the  economy  of  such  design  as 
opposed  to  the  fire-trap  methods  so  long  in  vogue  is  now 
being  daily  emphasized  by  architects,  engineers,  and  the 
technical  press.  And  what  is  most  gratifying  is  the  fact 
that  this  economy  is  beginning  to  be  appreciated  not  only 
by  the  owners  of  palatial  office  buildings,  stores,  and  mag- 
nificent residences,  but  also  by  people  of  limited  means,  as 
is  evidenced  by  the  start  already  made  in  fire-proofing  the 
ordinary  city  house,  at  a  figure  not  exceeding  the  cost  of 
present  methods.  It  was  found  recently,  in  taking  figures 
for  a  building  in  Philadelphia  to  cost  $125,000,  that  a  thor- 
oughly fire-proofed  construction  would  cost  only  3.6  per 
cent  more  than  the  ordinary  method  of  building.  This  in- 
crease would  be  compensated  for  in  a  very  short  time  by 
the  decreased  insurance. 

The  tide  has  turned,  and  nothing  can  stay  the  flood  of 
progress  in  this  direction.  The  dawn  of  the  twentieth  cen- 
tury will  undoubtedly  see  nearly  all  of  our  mercantile, 
manufacturing,  and  even  dwelling  houses,  except  those  of 


FIRE  PROTECTION.  II 

the  very  cheapest  description,  built  according  to  fire-resist- 
ing principles.  Steel,  the  clay  products,  and  cement  or 
concrete  are  the  materials  of  the  future,  permanent,  fire- 
resisting,  of  ready  adaptability,  and  of  remarkably  low  cost. 
The  fire-trap  timber  construction,  threatening  the  exhaus- 
tion of  our  vast  forestry  resources,  accompanied  by  its 
susceptibility  to  dampness,  drought,  heat,  and  cold,  involv- 
ing dry-rot,  as  shown  by  the  collapse  some  years  ago  of  a 
prominent  hotel  in  Washington,  must  give  way  to  new  con- 
ditions, and  further  improvement  in  a  field  of  such  promise. 
The  insurance  burden  will  be  gradually  lightened,  and 
human  life  be  better  protected. 

While  buildings  could  be  erected  with  absolutely  no 
inflammable  material  in  their  construction,  there  would 
still  remain  the  furniture  and  property  of  the  tenants  to 
feed  possible  fire.  This  element  of  danger  cannot  be  elimi- 
nated ;  and  added  to  this  are  the  dangers  that  come  from 
without  as  well  as  from  within.  For  as  long  as  highly  in- 
flammable buildings  surround  even  the  most  excellent  of 
modern  fire-proof  structures  the  term  is  but  mockery. 
Fire-proof  structures  must  stand  in  fire-proof  cities.  Hence 
the  word  "  fire-proof,"  as  applied  to  modern  structures,  does 
not  mean  one  that  claims  immunity  from  all  danger  of  fire, 
for  considerable  woodwork  must  still  be  used  in  interiors, 
and  the  average  contents  are  dangerous  in  the  extreme  ; 
but  it  does  claim  to  embody  principles  which  have  reduced 
the  fire  hazard,  both  interior  and  exterior,  to  a  minimum, 
according  to  the  best  skill  and  judgment  of  the  day.  The 
term  implies  that  all  structural  parts  of  the  edifice  must  be 
formed  entirely  of  non-combustible  material,  or  material 
which  will  successfully  withstand  the  injurious  action  of 
extreme  heat.  Following  is  the  definition  given  in  the 
new  building  ordinance  of  Chicago:  "  The  term  'fire-proof 
construction  '  shall  apply  to  all  buildings  in  which  all  parts 


12 


ARCHITECTURAL  ENGINEERING. 


that  carry  weights  or  resist  strains,  and  also  all  stairs  and 
all  elevator  enclosures  and  their  contents,  are  made  entirely 
of  incombustible  material,  and  in  which  all  metallic  struc- 
tural members  are  protected  against  the  effects  of  fire  by 
coverings  of  a  material  which  must  be  entirely  incom- 
bustible and  a  slow  heat-conductor.  The  materials  which 
shall  be  considered  as  fulfilling  the  conditions  of  fire-proof 
coverings  are  :  First,  brick ;  second,  hollow  tiles  of  burnt 
clay  applied  to  the  metal  in  a  bed  of  mortar,  and  con- 
structed in  such  manner  that  there  shall  be  two  air-spaces 
of  at  least  three-fourths  of  an  inch  each  by  the  width  of  the 
metal  surface  to  be  covered,  within  the  said  clay  covering ; 
third,  porous  terra-cotta,  which  shall  be  at  least  two  inches 
thick,  and  shall  also  be  applied  direct  to  the  metal  in  a  bed 
of  mortar;  fourth,  three  layers  of  plastering  on  metal  lath, 
so  applied  upon  metal  furring  that  there  shall  be  a  solid 
layer  of  mortar  at  least  one-half  inch  thick  between  the 
metal  to  be  covered  and  the  metallic  lath,  and  then  two  air- 
spaces of  at  least  three-fourths  of  an  inch  in  the  clear  be- 
tween the  first-mentioned  layer  of  plastering  and  the  outer 
surface  of  the  finished  covering." 

There  are  many  materials  quite  satisfactory  as  fire- 
proofing  mediums  for  the  constructional  parts  of  a  building, 
but  the  inventor  has  yet  to  supply  an  acceptable  incom- 
bustible material  for  the  interior  finish.  The  best  that  can 
be  done,  at  present,  is  to  reduce  the  inflammable  elements 
to  a  minimum,  and  endeavor  to  confine  the  fire  by  means  of 
fire-proof  floors  and  partitions,  so  that  it  may  do  no  injury 
beyond  the  consumption  of  local  woodwork  and  furnish- 
ings. This  may  be  accomplished  largely  by  means  of 
floors  of  concrete  or  terra-cotta  with  I-beams,  using  mosaic 
or  marble  tile  instead  of  wood  flooring,  partitions  of 
plaster  board,  cement  or  metallic  lath,  or  terra-cotta  blocks, 
and  bases  and  wainscoting  of  marble.    The  possibility  of 


FIRE  PROTECTION.  13 

using  frames  and  casings  for  doors  and  windows  made 
either  of  metal  or  sheet  metal  over  wood,  and  doors 
covered  with  sheet  metal,  seems  but  a  question  of  short 
time  in  adding  further  efficiency  to  high-class  fire-proof 
structures.  A  metal-covered  door  has  lately  been  intro- 
duced in  this  country,  giving  a  well-appearing,  light,  and 
incombustible  contrivance,  and  serving  as  an  effectual 
barrier  against  the  spread  of  flames.  The  success  that  has 
attended  the  use  of  wire  glass  in  skylights  has  also 
prompted  the  suggestion  to  reduce  the  exterior  hazard  by 
protecting  all  windows,  which  offer  the  most  vulnerable 
points  of  attack,  by  using  a  plate  glass  with  silvered  or 
gilded  wires  imbedded  therein,  in  graceful  patterns  or  net- 
work, serving  the  purpose  of  additional  fire  protection,  as 
well  as  architectural  effect.  The  planning  of  the  building, 
and  the  proper  location  and  installation  of  the  various 
power  plants  and  mechanical  features,  also  become  vital 
problems  in  fire-proofing. 

The  success  that  has  attended  past  efforts  in  this  direc- 
tion may  be  judged  by  such  examples  of  fire  as  have  been 
afforded  in  protected  structures.  The  largest  and  most 
interesting  of  such  tests  of  the  new  methods  was  the  burn- 
ing of  the  Chicago  Athletic  Club  building  while  under 
construction.  Though  not  entirely  satisfactory  as  a  test  of 
present  building  methods,  "  this  building  furnishes  an  assur- 
ance that  was  lacking  before — that  the  metal  parts  of  a 
building  if  thoroughly  protected  by  fire-proofing,  properly 
put  on,  will  safely  withstand  any  ordinary  conflagration,  if 
the  quantity  of  combustible  materials  the  building  contains 
is  not  greatly  in  excess  of  that  which  enters  into  the  con- 
struction of  the  building  itself." 

This  extract  from  the  report  of  experts  employed  to 
investigate  this  fire  and  its  effects,  emphasizes  two  very 
important  facts,  namely,  the  danger  of  the  indiscriminate 


14 


ARCHITECTURAL  ENGINEERING. 


use  of  combustible  material  not  absolutely  necessary  in  the 
construction,  and  second,  the  evident  superiority  of  terra- 
cotta as  a  fire-proofing  substance. 

The  above  fire,  which  occurred  on  November  r,  1892, 
was  the  first  case  on  record  of  a  fire  in  a  building  intended 
to  be  fully  fire-proof  where  the  loss  to  the  insurance  com- 
panies was  more  than  thirty  per  cent  of  its  value.  It  is 
further  stated  in  the  report  that  "  if  the  building  had  been 
completed,  it  would  never  have  contained  combustible 
material  enough  (or  so  distributed)  to  have  produced  suffi- 
cient heat  to  have  done  any  considerable  damage  to  the 
building  by  burning." 

The  fire  in  question  was  of  very  intense  heat,  inasmuch 
as  a  vast  quantity  of  scaffolding,  flooring,  trim,  etc.,  was 
collected  in  mass,  preparatory  to  use  ;  but,  in  spite  of  this, 
there  seemed  no  reason  for  questioning  the  integrity  and 
strength  of  the  building,  as  a  whole,  after  the  fire,  and  no 
doubt  existed  that  the  fire-proofing  around  the  columns 
saved  them  from  utter  collapse,  because  it  remained  in 
place  until  the  fuel  that  had  fed  the  flames  was  well-nigh 
exhausted.  The  result  to  the  building  included  the  entire 
destruction  of  all  the  interior  finish,  plastering,  piping,  and 
wiring,  as  well  as  parts  of  the  elaborate  front  of  Bedford 
stone  and  pressed  brick.  But  the  steel  columns  and  beams 
were  uninjured,  except  a  few  of  the  latter  where  unpro- 
tected ;  and  the  tile  arches,  built  after  the  end  construction 
method,  were  almost  uninjured,  in  spite  of  the  combined 
action  of  great  heat  and  frequent  applications  of  cold 
water. 

It  is  not  advocated  that  fire-proofing  as  efficient  (or  in- 
efficient when  the  preservation  of  human  life  is  considered) 
as  the  foregoing  example  is  sufficient  for  present  needs — 
it  certainly  is  not.  But  certain  underlying  facts  have  been 
clearly  proved  by  this  test,  and  taking  these  essential  points 


FIRE  PROTECTION.  I  5 

as  a  basis,  and  using  the  utmost  care  and  judgment  in  the 
matter  of  details,  it  must  be  admitted  that  the  use  of  terra- 
cotta, as  seen  in  the  better  examples  of  recent  fire-proof 
buildings,  goes  a  long  way  in  the  successful  solution  of  one 
of  the  most  important  problems  of  modern  times. 

The  method  of  fire-proofing  now  employed  consists  of 
a  vital  skeleton  or  frame-work  of  wrought  iron  or  mild 
steel,  enclosed  in  a  continuous  sheathing  of  terra-cotta. 
Every  square  inch  of  the  metal-work  must  be  protected  by 
means  of  the  various  shapes  made  by  the  terra-cotta  com- 
panies, thus  avoiding  all  direct  transfer  of  heat. 

Hollow  tile  as  a  building  material  was  first  introduced 
in  the  United  States  in  1871,  shortly  after  the  great 
Chicago  fire.  Its  first  use  was  for  floor  arches,  to  replace 
the  old  brick  arch  method.  Terra-cotta  was  a  direct  out- 
come from  conditions  imposed  by  the  increased  height, 
and  hence  weight,  of  a  rapidly  developing  architectural 
construction,  and  its  necessity  was  doubtless  made  more 
apparent  by  the  great  object  lesson  afforded  by  Chicago's 
disastrous  conflagration.  A  substance  was  necessary  to 
replace  the  heavy  masses  of  masonry  which  constituted  the 
fire-proofing  at  that  date,  both  in  the  exterior  walls  and  in 
floor  arches,  and  the  peculiar  advantages  of  terra-cotta 
caused  it  to  undergo  many  improvements  in  rapid  succes- 
sion, effecting  not  only  its  use  in  floor  construction  and 
column  and  beam  protection,  but  adapting  it  to  the  needs 
of  a  lighter  and  more  rapid  construction  throughout.  Its 
attendant  reduction  in  weight,  its  great  fire-resisting  quali- 
ties, its  peculiar  adaptability  to  all  conditions  of  position 
and  form,  its  susceptibility  to  modelling,  and  its  readiness 
of  manufacture  in  shapes  convenient  for  transportation  and 
erection,  soon  caused  it  to  win  favor  both  for  its  artistic 
possibilities  and  its  enduring  qualities,  through  which  it 
becomes  one  of  our  most  valuable   constructive  media. 


i6 


ARCHITECTURAL  ENGINEERING. 


First  used  in  interior  work  only,  it  soon  appeared  in  belt 
courses,  sills,  caps,  ornamental  panels  and  modelled  work 
in  the  hard-finished  terra-cotta,  until  to-day  its  use  is  almost 
more  general  than  stone,  appearing  in  entire  fronts,  as  a 
bold-faced  impersonation  of  solidity  itself. 

The  field  of  architectural  expression  in  terra-cotta  has 
recently  been  widened  to  a  still  more  remarkable  degree 
by  the  successful  completion  in  enamelled  terra-cotta  of 
the  facades  of  the  Reliance  Building,  Chicago,  supplied  by 
the  Northwestern  Terra-Cotta  Co.  (see  Fig.  i).  Should 
this  material  successfully  withstand  our  severe  climatic 
changes,  and  undergo  the  same  course  of  rapid  improve- 
ment as  did  the  ordinary  terra-cotta  used  in  exteriors,  a 
vast  field  for  more  extensive  coloring  effects  would  then  be 
opened  up  to  the  architect  who  strives  to  create  "  a  thing 
of  beauty  forever"  in  the  smoke  and  soot-laden  air  of  our 
American  cities.  The  underlying  idea  of  enamelled  ex- 
teriors is,  of  course,  that  they  may  be  readily  washed  down 
and  cleansed  of  the  soot  which  so  soon  destroys  any  at- 
tempts at  light  coloring. 

With  this  general  review  of  the  fire  problem,  and  terra- 
cotta as  a  weapon  of  defence,  it  becomes  evident  that  a  fire- 
proof structure  must  possess  : 

1.  General  excellence  of  design. 

2.  All  floors  of  fire-proof  construction. 

3.  All  columns  of  masonry  or  steel,  protected  from  fire. 

4.  All  outside  piers  and  walls  of  masonry  or  steel,  pro- 
tected from  fire. 

5.  All  partitions  and  furring  of  fire-proof  construction. 
There  are  three  methods  of  general  design  advocated 

at  the  present  time  as  means  of  reducing  the  fire  risk — the 
"  slow  burning  construction,"  the  so-called  "  mill  construc- 
tion," and  the  still  more  effectual  "fire-proof  construction." 
The  term  "  slow  burning  construction  "  is  applied  to  build- 


Fig.  i. — The  Reliance  Building.    D.  H.  Burnham  &  Co.,  architects. 


1 8 


ARCHITECTURAL  ENGINEERING. 


ings  in  which  the  structural  members,  carrying  the  floor 
and  roof  loads,  are  made  of  combustible  material,  but 
protected  throughout  from  injury  by  fire,  by  means  ol 
coverings  of  incombustible,  non-heat-conducting  materials. 
Thus  the  wooden  floor  joists  are  protected  on  the  under 
side  by*  a  single  covering  of  plaster  on  metal  lath,  while  a 
thickness  of  \\  inches  of  mortar  or  incombustible  deaden- 
ing is  required  above  the  joists.  Columns,  if  of  oak,  with 
a  sectional  area  of  100  square  inches  or  over,  need  not  have 
special  fire-proof  coverings.  Partitions  and  elevator  en- 
closures must  be  wholly  of  incombustible  material,  and  no 
wood  furring  is  allowed. 

Buildings  of  "  mill  construction  "  are  those  in  which  all 
floor  and  roof  joists  and  girders  have  a  sectional  area  of  at 
least  72  square  inches,  with  a  solid  timber  flooring  not  less 
than  3f  inches  in  thickness.  Columns  of  wood  need  not  be 
protected,  but  they  should  have  a  sectional  area  of  at  least 
100  square  inches.  Partitions  and  elevator  enclosures  are 
of  incombustible  material,  and  no  wooden  furring  or  lath- 
ing is  used. 

"  Fire-proof  construction"  has  already  been  defined.  The 
two  types  first  mentioned  do  not,  then,  depend  on  the  use  of 
materials  wholly  incombustible,  but  rather  on  the  judicious 
design  and  careful  use  of  ordinary  building  materials,  the 
aim  being  to  provide  structures  so  open  and  free  from 
fire-lurking  corners  that  they  may  offer  no  obstacles  to  a 
speedy  suppression  of  the  conflagration.  These  types  are 
peculiarly  adapted  to  large  mills,  warehouses,  and  the  like. 

The  scientific  fire-proofing  of  a  building  does  not  con- 
sist in  a  proper  selection  of  materials  alone,  for  a  structure 
may  be  reasonably  secure  against  accidental  fire,  or  the 
extension  of  fire,  even  when  built  of  combustible  materials ; 
nor  does  it  lie  merely  in  guarding  against  the  causes  of 
fire.    It  can  be  secured  only  by  a  thorough  acquaintance 


FIRE  PROTECTION.  19 

with  all  the  general  features  and  minutest  details  of  all 
kinds  of  structures,  and  by  a  quick  perception  "  for  the 
numerous  elements  of  danger  that  are  constantly  creeping 
into  modern  systems  of  buildings."  The  plan  must  be 
carefully  studied  to  secure  means  of  cutting  off  communi- 
cation between  floor  and  floor,  and  between  and  around 
dangerous  sources,  isolating,  if  possible,  all  stairways  and 
elevator-shafts  by  means  of  fire-resisting  walls,  and  con- 
fining all  power  and  mechanical  plants  in  such  a  way  that 
there  can  be  no  possible  means  of  fire  extension.  It  is  true 
that  most  high  office  buildings  do  not  possess  the  isolated 
stair-well  or  elevator-shaft,  but  if  they  do  not,  great  care 
must  be  taken  in  making  the  halls  and  corridors  of  more 
than  ordinary  security.  They  will  still  be  the  means  for  a 
rapid  distribution  of  smoke  from  floor  to  floor,  and  thus 
make  the  danger  from  suffocation  assume  an  importance 
equal  to  that  of  fire.  This  threatening  possibility  has  not 
yet  verified  itself,  and  it  is  to  be  hoped  that  it  will  be 
denied  the  opportunity. 

No  less  important  is  the  cutting  oft  ol  all  communica- 
tion between  pipe-  and  air-passages.  Piping  and  passages 
of  all  kinds  should  be  carefully  considered  as  a  part  of  the 
fundamental  design,  for  they  not  only  become  great  eye- 
sores from  their  exposed  positions  in  offices,  but  they  also 
serve  to  make  many  of  our  fire-proofing  endeavors  quite 
useless. 

The  architect  or  engineer  must  finally  be  well  informed 
in  regard  to  the  details  and  varied  uses  of  approved  fire- 
proofing  materials.  These  must  include  terra-cotta  in  all 
the  different  shapes  made  by  the  terra-cotta  companies, 
cement,  concrete,  fire-brick,  asbestos,  mackolite,  etc.  A 
judicious  and  economic  use  of  all  these  materials  is  neces- 
sary, so  that  the  most  practicable  form  may  be  chosen  to 
secure  the  desired  end. 


20 


A  R CHI TE  C T  URA  L  ENGINEERING . 


Some  of  these  important  minutiae  may  properly  receive 
detailed  attention,  when  we  remember  that  the  strength  of 
a  structure  is  gauged  by  its  weakest  point. 

The  metal  columns,  for  example,  are  properly  figured 
for  their  safe  dimensions,  but  from  this  step  on  they  are 
apt  to  become  a  bug-bear  to  both  architect  and  owner,  the 
former  desiring  to  reduce  their  size  to  a  minimum  on 
account  of  appearance,  while  the  latter  considers  that  they 
deprive  him  of  the  revenue  of  just  so  much  floor-space. 
Any  measures  are  therefore  adopted  to  reduce  their  size. 
First,  the  various  waste-,  heat-,  and  supply-pipes  are  run  up 
alongside  the  columns  from  floor  to  floor.  For  the  passage 
of  these  pipes  openings  must  be  made  in  the  tile  floor 
arches,  which,  in  the  rush  of  building  operations,  may  never 
be  properly  filled  up  again.  These  openings  come  inside 
the  line  of  the  fire-proof  slabs  of  the  column,  thus  forming 
one  long  continuous  flue  from  basement  to  roof.  The 
finished  line  of  the  fire-proofed  and  plastered  column  is 
often  not  more  than  2  in.  from  the  extreme  points  of  the 
metal-work,  and  then,  deducting  J  in.  or  f  in.  for  plaster, 
little  enough  is  left  for  the  fire-proofing  proper.  The 
various  pipes  before  mentioned  will  very  often  project 
even  farther  than  the  column  itself,  thereby  tempting  the 
fire-proofer  to  trim  and  shave  till  the  original  little  has  be- 
come still  less. 

In  the  Athletic  Club  Building  fire  some  of  these  points 
were  illustrated  with  glaring  prominence.  A  steel  frame- 
work and  fire-proof  covering  having  been  used  as  the 
main  elements  of  construction,  further  consideration  of  fire 
hazards  were  apparently  slighted.  In  no  case  did  the  fire- 
proofing  extend  more  than  2  in.  from  the  outermost  edge 
of  the  ironwork,  while  wooden  nailing-strips  were  em- 
bedded in  the  tile  at  intervals  of  about  3  ft.  starting  from 
the  floor  (a  4-in.  face  exposed),  making  successively  3  ft.  of 


FIRE  PROTECTION.  21 

tile  and  4  in.  of  wood.  These  nailing-strips  were  employed 
as  grounds  for  the  panelled  oak  wainscoting,  and  a  further 
error  was  made  in  leaving  an  air-space  behind  this  panel- 
ling, with  no  "  back  "  plastering.  The  ceiling  also  left  an 
air-space,  due  to  i-in.  raised  nailing-strips. 

As  a  matter  of  course  the  wooden  grounds  around  the 
column  burned  out,  letting  the  fire-proofing  fall  in  3-foot 
sections.  It  so  happened  that  but  two  columns  were 
badly  bent  by  the  intense  heat,  but  who  can  say  what  the 
stability  of  those  re-used  unbent  columns  really  is?  Were 
they  cooled  slowly,  or  suddenly  by  the  application  of 
streams  of  water,  and  thus  rendered  brittle,  and  were  they 
heated  unevenly,  thus  causing  great  strain  in  the  material 
on  but  one  side  of  the  column?  What  was  the  amount  of 
expansion  and  contraction  ?  No  experiments  could  be 
made  with  reasonable  economy  and  safety  to  satisfy  these 
queries,  leaving  the  present  state  of  the  building  an  un- 
certain conjecture. 

The  proper  installation  and  distribution  of  the  mechani- 
cal features  in  a  modern  office  building  have  been  given 
considerable  attention  by  John  M.  Carrere  (see  Eng.  Mag., 
October,  1892),  and  the  system  proposed  by  him  will  un- 
doubtedly add  greatly  to  the  efficiency  of  fire-proofing,  and 
remedy  many  of  the  weak  details  just  considered.  In 
order  to  avoid  chases,  or  continuous  flues,  the  lowering  of 
the  hall  ceilings  is  suggested,  "  thereby  obtaining  a  hori- 
zontal space  under  the  floors  of  the  halls  at  each  story, 
lined  and  fire-proofed,  where  all  the  mechanical  features 
except  steam  heat  can  be  placed  "  (see  Fig.  2).  An  arrange- 
ment of  this  character  would  certainly  possess  many  great 
advantages — it  would  always  be  accessible  for  repairs,  easy 
of  connection  with  all  offices,  and  would  serve  as  a  safe 
and  at  the  same  time  hidden  conduit  for  all  wiring,  pip- 
ing, and  ventilating  air-ducts,  either  exhaust  or  indriven. 


22 


ARCHITECTURAL  ENGINEERING. 


The  additional  expense  would  .not  be  great  either,  and 
when  its  permanency  is  considered,  never  being  affected 
bv  the  moving  of  partitions,  etc.,  as  is  now  the  case,  it  is 
surprising  that  such  a  system  has  not  attained  more 
general  use. 

At  the  ends  of  these  horizontal  ducts  are  vertical  chases 
or  ducts  built  solidly  of  fire-proof  blocks  or  brick  from 
cellar  to  roof,  and  connected  at  each  floor  with  the  hori- 


OFFICE 


OFFICE 


OFFICE 


VENT. 
OFFICE 


Fig.  2. 


zontal  leads,  but  still  partitioned  off  at  each  floor  with  wire 
and  plaster  partitions,  to  prevent  the  spread  of  possible 
fire.  All  of  the  vertical  risers  could  be  placed  in  these 
chases,  thus  avoiding  the  unsightliness  of  pipes  in  the  office 
space,  or  the  necessity  of  placing  such  piping  within  the 
column  space. 

The  growing  importance  of  adequate  fire  protection 
may  be  judged  from  the  care  displayed  in  the  encasing  of 
the  large  girders  at  the  new  Tremont  Temple  in  Boston. 
These  girders  carry  columns  of  great  load,  and  any  warp- 
ing tendency  from  great  heat  would  be  attended  by  most 
serious  results.  The  steel  girders  were  first  surrounded 
by  blocks  of  terra-cotta  on  all  sides,  and  these  blocks 
were  then  bound  by  iron  bands.  Over  these  blocks  was 
stretched  expanded  metal  lathing  with  a  heavy  coat  of 


FIRE  PROTECTION. 


23 


Windsor  cement.  Iron  furring  was  next  placed  on  all  sides 
to  receive  a  second  layer  of  expanded  metal  lath,  on  which 
was  placed  the  finished  plaster.  The  covering  thus  con- 
sisted of  a  dead  air-space,  terra-cotta  blocks,  a  coating  of 
cement,  a  second  air-space,  and  an  external  coating  of 
cement. 


CHAPTER  III. 


SKELETON  CONSTRUCTION— EXAMPLES,  ERECTION,  ETC. 

Many  of  the  details  which  will  be  discussed  in  the  fol- 
lowing pages  may  be  better  appreciated  in  their  relation 
to  the  whole  subject  if  a  few  typical  skeleton  structures 
are  examined.  The  scope  of  this  outline  will  not  permit  of 
a  discussion  of  the  architectural  problems  involved  in  the 
design  of  a  modern  office  building,  hotel,  or  any  of  the 
structures  which  are  now  built  according  to  skeleton 
methods.  The  points  here  considered  are,  rather,  those  of 
construction  pure  and  simple.  But  the  comprehensive 
view  of  the  subject  necessary  to  the  architect  or  architec- 
tural engineer  may  only  be  obtained  through  an  accurate 
knowledge  of  the  manifold  items  which  become  a  part  of  a 
successful  plan.  These  accessories  to  the  mere  frame-work 
lie  within  the  province  of  the  engineer  as  well  as  of  the 
architect,  and  here,  as  in  the  execution  of  the  external  ex- 
pression of  architectural  engineering,  a  perfect  harmony 
must  exist  between  the  two  branches  in  the  perfection  of 
all  mechanical  details,  if  results  are  to  be  secured  which 
may  be  looked  upon  as  creditable  to  both  professions. 

The  value  of  such  accessories  may  be  more  fully  real- 
ized when  the  self-sufficiency  of  a  modern  office  building, 
containing  all  modern  improvements,  is  considered.  Elec- 
tric light,  the  telephone,  mail-chutes,  and  well-appointed 
toilet-rooms  are  already  demanded  as  absolute  necessities, 
while  late  examples  provide  telegraph  and  messenger  ser- 
vice,  cigar-  and    news-stands   and    barber-shops,  besides 

24 


/ 


SKELETON  CONSTRUCTION.  2$ 

restaurants  and  cafes  in  the  basements.  It  is  true  that 
many  of  these  factors  would  seem  to  have  little  bearing  on 
the  duties  of  the  engineer,  and  yet  it  was  just  such  condi- 
tions, imposed  on  the  designer  of  the  foundations  of  office 
buildings,  that  produced  the  successful  development  of  the 
so-called  raft  or  floating  foundations,  in  order  that  the  base- 
ments might  be  unencumbered  by  the  large  pyramidal 


Fig.  3. — Chicago  Stock  Exchange.    Adler  &  Sullivan,  architects. 


masses  of  stone  previously  used  as  footings,  and  the  base- 
ment space  might  be  added  to  the  available  renting  area,  or 
be  used  for  the  mechanical  plants.  The  rigid  economy  of 
floor  space  which  is  demanded  may  only  be  obtained  by 
careful  attention  to  the  most  advantageous  uses  to  which 
the  different  floors  and  rooms  in  the  structure  may  be  put. 

Some  examples  of  office  buildings  recently  constructed 
in  Chicago  will  here  be  given. 


26 


ARCHITECTURAL  ENGINEERING. 


THE  CHICAGO  STOCK  EXCHANGE. 

A  perspective  of  this  building  by  Adler  &  Sullivan, 
architects,  is  shown  in  Fig.  3.  The  facades  are  constructed 
of  a  yellow-drab  terra-cotta,  with  white  enamelled  brick  in 
the  interior  court. 

Fig.  4  shows  the  basement  plan,  containing  the  boiler- 
and  engine-rooms,  restaurants,  etc. 

Fig.  5  is  a  plan  of  the  ground  floor,  showing  the  en- 
trance vestibules,  elevators,  store  areas,  etc. 

Fig.  6  gives  a  plan  of  the  arrangement  of  the  offices, 
etc.,  on  the  sixth  floor.  The  toilet-rooms,  barber-shop,  vent 
spaces,  and  the  arrangement  of  the  lighting  courts  are  plainly 
shown. 

THE  MARQUETTE  BUILDING. 

This  office  building  (see  Fig.  7),  designed  by  Messrs. 
Holabird  &  Roche,  architects,  has  but  just  been  completed. 
The  exterior  walls  are  built  mainly  of  a  dark  red  brick,  with 
terra-cotta  base,  cornice,  and  trimmings. 

A  typical  floorplan,  showing  possible  sub-divisions,  is 
given  in  Fig.  8.  Many  of  the  floors  in  the  larger  office 
buildings  are  never  subdivided  until  rented,  in  order  that 
the  arrangement  of  offices  may  be  made  to  suit  the  tenant. 

RELIANCE  BUILDING. 

Fig.  9  gives  a  typical  floor  plan  of  this  building  by 
D.  H.  Burnham  &  Co.,  architects.  This  arrangement  of 
offices  is  intended  for  rooms  to  be  used  in  suites.  The 
pipe  space  at  the  side  of  the  elevators,  and  the  space  for 
counterweights  behind  the  elevators,  are  plainly  shown,  as 
is  the  circular  smoke  flue. 

The  elevator  accommodations  in  these  various  buildings 
may  be  seen  on  the  plans.  Rapid  passenger  and  freight 
service  must  both  be  provided  for,  and  the  necessary  space 
allowed  for  the  hydraulic  cylinders  in  the  basement,  as 
well  as  for  the  vertical  counterweights.    Beams  must  be 


/}LLEY 


Fig.  7. — The  Marquette  Building.    Holabird  &  Roche,  architects. 


ARCHITECTURAL  ENGINEERING. 


Fig.  9.— Typical  Office  Floor  Plan  of  the  Reliance  Building. 


SKELETON  CONSTRUCTION.  33 

supplied  to  support  the  elevator  sheaves,  and  water-tanks 
located  to  supply  the  hydraulic  cylinders. 

If  the  basement,  as  in  Fig-.  4,  lies  below  the  sewer  level, 
and  it  is  to  be  occupied  by  stores,  cafes,  or  by  the  boiler- 
and  engine-rooms,  an  ejector  pit  will  be  necessary  to  raise 
the  sewage  to  the  proper  level.  Pumps  for  water-supply, 
dynamos  for  electric  light,  boilers  and  steam  plant  for 
power  and  heating — all  must  be  definitely  determined 
and  carefully  weighed  in  their  relation  to  the  character  of 
the  building,  and  as  affecting  the  design  of  foundations  and 
all  structural  details. 

The  following  data  may  be  of  interest  as  descriptive  of 
some  of  the  mechanical  furnishings  of  one  of  Chicago's 
most  celebrated  office  buildings,  the  Masonic  Temple, 
shown  in  Fig.  10. 

The  entire  drainage  is  carried  through  the  building  by 
means  of  a  system  of  vertical  risers,  about  one  half  of  which 
connect  directly  with  the  street  mains,  through  piping 
suspended  from  the  basement  ceiling.  The  remainder  of 
the  risers,  and  all  drainage  from  the  boiler-room  and  base- 
ment space,  are  connected  by  a  system  of  underground 
piping,  with  two  50-gallon  Shone  ejectors,  placed  in  a  pit 
in  the  basement,  from  which  the  sewage  is  forced  to  the 
street  sewer.  This  was  necessary  in  order  to  keep  the 
basement  stores,  cafes,  etc.,  free  from  exposed  pipes.  All 
vertical  pipes  in  the  building,  both  for  water-supply  and 
drainage,  were  carried  in  fire-proof  pipe-spaces  especially 
provided.  The  water-supply  is  pumped  from  the  city 
mains,  by  pumps  located  in  the  basement,  to  storage  tanks 
on  the  twentieth  floor,  with  a  combined  capacity  of  7000 
gallons.  On  the  twentieth  floor  also  are  four  compression 
elevator  tanks  of  18,500  gallons  capacity  total.  For  elevator 
and  water-supply  service  seven  pumps  are  required,  having 
a  total  capacity  of  from  2000  to  3800  gallons  per  minute. 


34 


A R CHJTE C T URA  L  ENG INEERING, 


Fig.  io.— The  Masonic  Temple.    Burnham  &  Root,  architects. 


SKELETON  CONSTRUCTION. 


35 


Each  office  and  store  has  a  private  wash-basin,  with  gen- 
eral  toilet-rooms  and  barber-shop  on  the  nineteenth  floor. 
The  main  toilet-room  contains  64  closets,  besides  addi- 
tional rooms  on  the  third  and  twelfth  floors  and  in  the  base- 
ment, with  from  8  to  18  closets  each. 


IflHB! 


Wm 


■Jut 


sHi  Mil 


iliiK: 


3 


ail 


##  lap 


Fig.  ii.— The  New  York  Life  Insurance  Building.    Jenney  &  Mundie,  architects. 

Forty  thousand  square  feet  of  radiation  surface  are  re- 
quired, all  in  direct  radiation.  The  steam  is  supplied  on  the 
"  overhead"  system  through  16-in.  mains  running  directly 


36 


ARCHITECTURAL  ENGINEERING. 


to  the  attic,  thence  around  the  exterior  walls  and  down. 
Six  dynamos  supply  7000  16-candle-power  lamps.  For  the 
power  and  steam  plant  eight  horizontal  tubular  boilers  are 
used,  with  a  total  of  1000  horse-power. 

There  are  several  features  in  the  Masonic  Temple  de- 
sign worthy  of  especial  note.    Several  of  the  upper  floors 


Fig.  12. — Banking  Floor,  New  York  Life  Insurance  Building. 

are  devoted  to  Masonic  purposes,  and  the  large  assembly-, 
drill-  and  banquet-rooms  were  kept  free  from  columns  by 
spanning  the  areas  with  lattice  girders,  on  which  rest  the 
arched  ceiling  and  roof  trusses.  The  interior  court  also 
possesses  special  features  in  the  galleries  provided  at  each 


SKELETON  CONSTRUCTION.  37 

story  for  the  lower  ten  floors.  This  plan  was  intended  to 
attract  small  storekeepers  and  the  like  as  occupants  of  the 
adjoining  stores  or  offices,  thus  concentrating  many  trades- 


■*r*'  f  

o    o  /srcef 


FlG.  13. — Typical  Office  Floor  Plan,  New  York  Life  Insurance  Building. 

men  under  one  roof.    The  scheme  has  not  proved  a  success. 

The  roof  of  the  Masonic  Temple  is  covered  by  an  en- 
closure of  glass,  serving  as  a  summer-garden  and  place  of 
observation. 

NEW  YORK  LIFE  INSURANCE  BUILDING. 

A  perspective  of  this  building,  designed  by  Jenney  & 
Mundie,  architects,  is  shown  in  Fig.  11.    The  lower  three 


38 


ARCHITECTURAL  ENGINEERING. 


floors  are  built  of  granite,  with  brick  and  terra-cotta  above. 
The  plan  of  the  first  floor,  devoted  to  banking  purposes,  is 
shown  in  Fig.  12,  while  the  typical  office  plan  is  shown  in 
Fig.  13. 


Fig.  14. — The  Fort  Dearborn  Building.    Jenney  &  Mundie,  architects. 
FORT  DEARBORN  BUILDING. 

This  building,  shown  in  Fig.  14,  is  but  just  completed. 
It  was  designed  by  Jenney  &  Mundie,  architects,  and  a 
number  of  the  details  used  in  its  construction  will  be 


/ 


SKELETON  CONSTRUCTION.  39 

given  later.  The  typical  office  floor  plan  is  given  in 
Fig.  15. 

A  floor  plan  of  the  Champlain  Building,  Holabird  & 
Roche,  architects,  is  shown  in  Fig.  16. 

Fig.  17  gives  a  perspective  of  the  Old  Colony  Building, 
by  the  same  architects. 

These  examples  of  floor  plans  will  serve  to  show  the 
general  arrangement  of  offices,  halls,  and  entrances  in  build- 
ings very  recently  erected,  and  the  conditions  which  deter- 
mined the  general  features  of  construction  will  be  apparent, 
in  so  far  as  the  plan  may  affect  the  locations  of  the  columns, 
etc.  "  The  framing  plans  "  must  now  be  worked  out,  one 
for  each  floor,  showing  the  location  of  all  piers,  columns, 
girders,  beams,  etc.,  in  their  proper  positions,  with  all  the 
necessary  dimensions  and  sizes. 

Fig.  18  shows  a  framing  plan  of  the  third  floor  of  the 
Fort  Dearborn  Building. 

Fig.  19  is  a  framing  plan  for  the  sixth,  seventh,  and 
eighth  floors  of  the  Reliance  Building. 

The  increased  use  of  structural  steel,  as  indicated  in 
these  framing  plans,  has  found  the  architects,  to  a  great 
extent,  unprepared  to  solve  in  detail  many  of  the  prob- 
lems imposed  on  them.  They  have  been  forced,  in  work 
of  any  magnitude,  to  turn  the  details,  if  not  the  entire 
constructional  scheme,  into  the  hands  of  the  engineer, 
either  as  an  employe  or  co-partner.  The  ignorance  which 
the  average  architect  displays  in  connection  with  struc- 
tural iron  details  is  proverbial,  and  contractors  for  steel- 
work especially  have  long  indulged  in  considerable  sar- 
casm at  the  expense  of  the  architect  and  his  plans. 
When,  however,  this  work  is  intrusted  to  the  engineer,  it 
becomes  a  question  as  to  how  far  the  actual  work  of  detail- 
ing needs  to  be  carried,  after  the  computations  and  general 
framing  plans  are  made. 


4o 


ARCHITECTURAL  ENGINEERING. 


Fig.  15.- Typical  Office  Floor  Plan,  Fort  Dearborn  Building. 


42 


ARCHITECTURAL  ENGINEERING. 


Fig.  17. — The  Old  Colony  Building.    Holabird  &  Roche,  architects. 


SKELETON  CONSTRUCTION. 


43 


It  is  comparatively  seldom  that  complete  detail  plans 
for  the  steelwork  of  a  building  are  made  by  the  architect. 
Still  less  frequent  are  the  cases  where  such  detail  plans 
could  be  used  as  actual  shop  drawings  by  the  contractor, 


Fig.  18. — Typical  Framing  Plan  of  the  Fort  Dearborn  Building. 

as  in  nearly  every  case  the  manufacturer  much  prefers  to 
make  his  own  shop  drawings,  to  conform  to  the  usage  of 
his  own  plant.  The  architect  has  generally  been  content 
to  specify  the  sizes  and  weights  of  the  material  to  be  used, 


44 


ARCHITECTURAL  ENGINEERING. 


leaving  the  details  to  be  worked  out  by  the  contractor  with 
the  approval  of  the  architect. 

The  trained  engineer,  however,  is  not  usually  satisfied 


\#k"**3*imj-t,    !   1   ! 

£  1  — T  * 


pIG>  I9._ Typical  Framing  Plan  of  the  Reliance  Building. 

with  such  license  on  the  part  of  the  contractor,  and  the 
best  classes  of  work  are  made  in  accordance  with  definite 
details  furnished  by  the  engineer,  after  a  careful  considera- 


SKELETON  CONSTRUCTION.  45 

tion  of  the  conditions  to  be  fulfilled.  This  does  not  mean 
that  complete  shop  drawings  are  made,  but  rather  such 
connections  and  special  points  in  the  design  as  need  par- 
ticular attention.  The  balance  of  the  detailing  may  be 
made  to  suit  the  contractor,  with  the  approval  of  the  en- 
gineer, in  conformity  with  the  sizes  of  material  marked  on 
the  plan,  and  the  carefully  drawn  specifications. 

The  idea  of  allowing  the  manufacturer  to  prepare  com- 
plete details  after  his  own  general  scheme,  and  following 
specifications  only,  is  not  consistent  with  best  results,  in 
the  judgment  of  the  writer,  though  such  an  arrangement 
has  often  been  advocated.  It  is  true  that  it  has  been  a 
very  common  practice  with  bridge  engineers  to  furnish  the 
moving-load  diagram,  and  allow  the  bidders  to  design  the 
structure  as  they  saw  fit,  so  long  as  it  fulfilled  all  require- 
ments of  the  specifications.  This  has  probably  been  one 
reason  for  the  high  degree  of  excellence  shown  in  the  work 
of  the  better  bridge  companies,  as  each  bidder  endeavors 
to  use  his  material  to  the  best  possible  advantage.  Such 
a  practice,  however,  in  building  work  will  require  a  very 
careful  supervision  of  the  work  by  the  engineer,  and  as  the 
various  contractors  will  use  those  shapes  most  in  favor,  or 
of  least  cost,  at  their  particular  works,  the  calculations,  con- 
nections, details,  etc.,  must  all  be  gone  over  and  thoroughly 
checked,  that  all  conditions  may  be  satisfactory.  A  careful 
checking  is  necessary  in  any  case,  but  where  such  complete 
freedom  is  accorded  the  bidder,  it  will  rarely  be  that  he 
is  able  to  grasp  the  general  ensemble  in  such  a  manner  as 
to  make  satisfactory  details  in  the  required  time.  Again,, 
only  the  most  responsible  and  experienced  firms  could  be 
intrusted  with  such  a  task. 

Carefully  drawn  specifications,  complete  and  accurate 
framing  plans,  sufficient  spandrel  sections  and  any  special 
details,  with  all  sizes  and  dimensions  of  material,  will  insure 


46 


ARCHITECTURAL  ENGINEERING. 


rapid  and  satisfactory  work  on  the  part  of  the  iron  con- 
tractor. The  shop  drawings  may  then  be  examined,  and 
stamped  with  the  approval  of  the  engineer  as  received. 

ERECTION. 

In  skeleton  construction,  the  erection  of  the  framework 
progresses  very  rapidly  after  the  material  is  once  delivered 
on  the  ground.  All  punching  and  riveting  of  the  members 
is  done  at  the  shop,  leaving  only  the  assembling  and  field- 
riveting  to  be  done  on  the  ground,  besides  the  adjustment 
of  the  laterals.  Field-riveting  has  entirely  superseded  the 
use  of  bolts  in  the  best  class  of  work.  Bolt  connections 
were  tried,  but  were  soon  discarded  on  account  of  the 
cracks  which  developed  in  the  plastered  ceilings,  radiating 
from  the  column  connections  with  the  floor  system.  This 
was  due  to  the  play  of  the  bolts  in  the  holes. 

Steam  cranes  built  expressly  for  the  purpose  have  been 
used  in  some  cases  in  Chicago.  They  were  operated  on 
tracks  which  were  quickly  laid  over  the  floor  system,  and 
these  cranes  would  pull  themselves  up  an  incline,  from 
story  to  story,  as  fast  as  erected.  The  crane  boom  and  en- 
gine platform  revolved  on  a  pivot,  so  that  the  members 
required  very  little  handling.  The  old-fashioned  derricks 
or  gin-poles  are,  however,  generally  used,  some  contractors 
preferring  the  short  gin-pole,  erecting  one  story  at  a  time, 
while  others  use  a  large  boom  derrick,  setting  several 
stories  in  place  before  shifting  the  derrick.  The  erection 
of  ironwork  costs  from  $6  to  $8  per  ton. 

Two  stories  can  generally  be  erected  in  six  days  of  ten 
hours  each.  In  the  Unity  Building  of  seventeen  stories  the 
metal-work,  from  the  basement  columns  to  the  finished 
roof,  was  accomplished  in  nine  weeks. 

The  following  data  will  give  a  better  idea  of  the  ra- 
pidity of  building  operations  in  Chicago  as  shown  in  the 
erection  of  the  New  York  Life  Building: 


SKELETON  CONSTRUCTION.  47 

July  17.    Old  building  torn  down  to  grade. 

July  31.    Laid  out  new  footings. 

August  17.    Started  setting  basement  columns. 

August  31.    Started  laying  granite. 

September  5.    Started  setting  tile  arches. 

September  18.    Started  laying  terra-cotta  facing. 

September  29.    All  steel  set. 

November  9.    Tile  floors  all  set. 

November  11.    Terra-cotta  all  set. 

November  12.    Started  plaster. 

December  2.  Steam  plant  completed — turned  steam  on 
in  building. 

Of  the  671  individual  columns  in  this  building  but  a 
single  one  required  "  shimming."  A  thin  steel  wedged 
plate  was  used,  forged  to  fit.  The  columns  were  tested  for 
alignment  at  frequent  intervals.  An  average  of  twenty-five 
working  hours  was  required  to  set  the  steelwork  for  a 
complete  story. 

The  skeleton  or  "  veneer"  type  of  construction  possesses 
great  advantages  in  economy  of  time  required  for  erection, 
as  work  can  be  pushed  on  the  walls  at  different  stories  at 
one  and  the  same  time.  Thus  on  the  Manhattan  Building, 
Chicago,  the  main  cornice  of  terra-cotta  was  completed 
before  the  wall  was  built  up  beneath  it.  On  the  Unity 
Building  the  granite  base-wall  was  being  built  at  the  first 
and  second  stories,  the  pressed-brick  face  was  being  placed 
at  the  twelfth-floor  level,  while  the  hollow-tile  arches  were 
being  set  for  the  fifteenth  floor, — all  at  the  same  time. 

Several  gangs  of  men  may  frequently  be  seen  at  dif- 
ferent levels  on  a  single  front  of  a  building,  and  laying 
pressed-brick  by  electric  light  was  even  tried  on  the  Ash- 
land Block,  Chicago,  in  an  endeavor  to  complete  the  build- 
ing by  May  i  :  and  the  intention  was  to  make  up  for  this 
extra  expense  of  night-work  by  time  gained  through  leases 
signed  earlier  than  would  otherwise  have  been  possible. 


ARCHITECTURAL  ENGINEERING. 


Fig.  21. — The  Reliance  Building  during  Construction,  August  i,  1894. 


ARCHITECTURAL  ENGINEERING. 


Figs.  20  and  21  show  the  Reliance  Building  during  con- 
struction. 

PERMANENCY  OF  SKELETON  CONSTRUCTION. 

Aside  from  the  question  of  fire  resistance,  considerable 
discussion  has  arisen  of  late  concerning  the  permanency  of 
skeleton  construction.  This  controversy  between  friends 
and  indifferent  observers  of  skeleton  methods  has  been 
aggravated  by  the  reluctance  of  the  supervising  architect 
of  the  Treasury  seriously  to  consider  such  construction  as 
worthy  the  dignity  and  solidity  of  government  edifices — 
notably  in  the  proposed  new  Post-Office  building  for 
Chicago.  While  the  architectural  pros  and  cons  of  terra- 
cotta and  steel,  or  concrete  and  steel,  versus  solid  masonry 
construction  may  not  here  be  gone  into,  the  engineering 
side  of  this  matter  beer  nes  one  of  great  importance. 
Serious  as  it  is,  it  must  still  be  admitted  as  depending 
largely  on  personal  views,  for  the  want  of  reliable  data 
under  present  conditions.  Many  architects  are  not  slow 
to  pronounce  judgment  against  such  practice,  while  others 
warmly  champion  the  cause  of  steel  in  combination  with 
tile,  concrete,  or  cement.  The  divergence  of  present 
opinion  was  well  shown  in  a  recent  discussion  before  the 
American  Institute  of  x^rchitects  on  this  very  subject, 
where  examples  of  the  deterioration  of  iron  or  steel  under 
peculiar  conditions  were  emphatically  offset  by  instances 
of  remarkable  preservation  under  other  peculiar  condi- 
tions. The  point  would  then  seem  to  be  to  define  these 
conditions.  Prominent  Chicago  architects  and  engineers 
have  said  that  experience  seems  to  show  that  if  no  lime 
mortar  is  used  the  corrosion  of  the  metal  will  not  amount 
to  enough  to  be  of  any  danger,  while  others  point  to  the 
well-known  preservative  qualities  of  lime,  and  urge  its 
exclusive  use  in  connection  with  iron  or  steel.  Our  knowl- 
edge of  wrought  iron  or  steel,  therefore,  under  definite 


I 


SKELETON  CONSTRUCTION.  5  I 

variations  of  heat  and  moisture,  and  in  association  with 
limes,  cements,  and  concrete,  as  found  in  present  practice, 
must  continue  to  be  unsatisfactory  until  defined  by  more 
accurate  data.  Chicago  engineers  and  builders  show  their 
daily  faith  in  such  combinations  of  material,  and  this  type 
of  construction  is  rapidly  becoming  more  and  more  general 
in  the  United  States. 

The  effects  of  lime,  whether  as  one  of  the  ingredients  of 
mortar  or  limestone,  as  a  corrosive  factor  in  connection 
with  ironwork  seem  to  depend  very  largely  upon  the 
peculiar  conditions  of  each  particular  case.  Examples  are 
recorded  of  anchorage  cables  in  American  suspension 
bridges  which  were  found,  on  disclosure  after  some  years, 
to  be  partly  eaten  away  where  the  strands  had  come  into 
permanent  contact  with  the  limestone  masonry.  The  pres- 
ence of  water  was  possibly  accountable  for  this  corrosive 
action  ;  but  it  becomes  a  very  difficult  matter  to  construct 
masonry  which  will  allow  of  no  permeation  of  moisture, 
especially  in  walls,  piers,  or  foundations,  as  found  in  build- 
ing practice.  Dry  air  and  pure  water  produce  but  slight 
oxidizing  effects  on  iron  or  steel ;  "  but  when  the  former 
becomes  moist,  and  the  latter  impure  or  acidulated,  oxida- 
tion of  the  material  is  speedily  set  up,  and  when  once  com- 
menced, unless  the  process  is  arrested,  its  ultimate  destruc- 
tion becomes  a  simple  question  of  time."  The  use  of  lime 
mortar  would,  therefore,  seem  limited  to  localities  where  no 
fear  of  moisture  may  be  anticipated  ;  for  any  dampness  in 
combination  with  the  lime,  must  soon  show  its  effects  on 
the  metal-work. 

Considering  the  parts  of  a  skeleton  structure  which  are 
exposed  to  the  weather,  or  liable  to  the  presence  of  mois- 
ture, we  have :  all  exterior  walls,  piers,  etc.,  and  the  base 
ment  members,  including  foundations.    From  the  foregoing 
it  would  seem  that  lime  mortar  should  not  be  used  in  any 


5- 


ARCHITECTURAL  ENGINEERING. 


of  these  positions.  The  foundations  and  basement  walls, 
columns,  etc.,  are  either  surrounded  by  constant  moisture, 
or  by  wet  clay  or  earth  itself,  while  the  exterior  walls 
and  supporting  steelwork  are  subjected  to  the  climatic 
changes,  frost,  rain,  and  penetrating  dampness,  which  must 
sooner  or  later  pierce  the  terra-cotta  and  brick  envelope, 
and  so  reach  the  metal-work.  For  such  positions  cement 
mortar  should  undoubtedly  be  used  ;  it  seems  a  most  per- 
fect conservator  of  metal-work,  and  instances  are  recorded 
of  iron  found  in  perfect  condition  after  a  400-years'  entomb- 
ment in  cement  concrete  below  water.  Links  of  anchorages 
in  American  suspension  bridges  have  been  taken  up  after 
many  years  in  a  perfect  state  of  preservation  where  em- 
bedded in  cement.  A  further  recommendation  of  the  use 
of  cement  lies  in  the  fact  that  the  thermic  expansion  of 
Portland  cement  is  practically  the  same  as  that  of  iron — a 
fact  which  insures  perfect  cohesion  under  any  changes  of 
temperature. 

The  interior  members  of  the  framework  do  not  need  as 
careful  consideration,  being  maintained  at  a  more  uniform 
temperature,  and  protected  from  the  exterior  dampness. 
Interior  columns,  the  floor  system,  and  wind  bracing 
would,  therefore^  seem  safe  in  connection  with  lime  mortar, 
but  it  is  questionable  whether  the  best  work  should  not 
call  for  cement  mortar  and  even  cement  plaster  through- 
out. Cement  has  rapidly  cheapened  of  late  years,  and 
cement  plasters  are  largely  being  used  on  account  of  their 
better  fire-resisting  qualities. 

It  has  been  suggested  to  rely  entirely  on  the  preserving 
qualities  of  cement  rather  than  on  a  proper  painting  of  the 
metal-work.  Prof.  Bauschinger  states  that  his  experiments 
show  a  cohesion  between  iron  and  concrete  after  hardening 
of  from  570  to  640  lbs.  per  square  inch.  This  is  even  more 
than  the  tensiie  strength  of  the  best  concrete,  but  in  build- 


) 


SKELETON  CONSTRUCTION.  53 

ing  work  a  perfect  union  between  the  cement  mortar  and 
metal-work  can  never  be  attained  at  all  points,  and  a 
thorough  coating  of  paint  must  largely  be  relied  upon. 

All  constructive  ironwork  should,  therefore,  be  well 
coated  with  either  lampblack  mixed  with  oil,  or  red  lead 
and  linseed-oil.  The  very  best  of  materials  should  be  em- 
ployed. The  oxide  of  iron  or  mineral  paint  which  has 
generally  been  specified  for  all  painting  of  the  metal-work 
has  been  found  to  separate  from  the  steel,  and  form  an 
oxidation  of  the  metal  behind  the  paint.  A  mixture  of  red 
lead  and  linseed-oil  is  now  considered  as  the  best  protec- 
tive coating  for  iron  or  steel.  A  careful  inspection  of  all 
painting,  both  at  the  shop  and  in  the  field,  should  be  rigidly 
enforced. 

The  following  are  the  requirements  of  the  New  York 
building  law  in  regard  to  the  protection  of  iron  or  steel 
work  against  rust,  etc: 

"  Ail  ironwork  and  steelwork  used  in  any  building 
shall  be  of  the  best  material  and  made  in  the  best  manner, 
and  properly  painted  with  oxide  of  iron  and  linseed-oil 
paint  before  being  placed  in  position,  or  coated  with  some 
other  equally  good  preparation  or  suitably  treated  for 
preservation  against  rust." 

The  Chicago  ordinance  makes  no  mention  of  paint  or 
coatings  to  prevent  rust  in  the  metal  framework  except  as 
specified  for  fire-proofing  purposes  as  follows ;  "  In  all 
cases  the  brick  or  hollow  tile  shall  be  bedded  in  mortar 
close  up  to  tne  iron  or  steel  members,  and  all  joints  shall 
be  made  full  and  solid." 

The  Boston  law  requires  a  protection  from  heat  only, 
by  means  of  brick,  terra-cotta,  or  by  three  fourths  of  an 
inch  of  plastering. 

The  requirements  for  metal-work  in  foundations  are 
given  in  Chapter  XII. 


CHAPTER  IV. 


FLOORS  AND  FLOOR  FRAMING. 

There  is  scarce  a  subject  or  detail  in  the  present  field 
of  architectural  engineering  that  has  provoked  such  wide- 
spread attempts  at  improvement  and  perfection  as  the 
question  of  fire-proof  floor  systems.  The  present  day  is 
especially  prolific  in  new  patents  and  systems,  all  claiming 
a  complete  revolution  in  existing  methods,  until  both 
architect  and  engineer  alike  are  well-nigh  bewildered  in 
their  endeavors  to  keep  track  of  the  novelties  that  are  con- 
tinually being  presented  as  the  "cheapest  and  best"  solu- 
tion of  a  much-discussed  problem. 

A  proper  solution  cannot  be  realized  by  either  architect 
or  engineer  working  independently  of  each  other,  and  per- 
fection in  present  attempts  must  result  from  legitimate 
criticism  on  the  part  of  the  architect  as  to  the  adaptability 
of  the  material  to  exterior  form,  as  well  as  from  the  appli- 
cation of  the  laws  of  statics  as  demanded  by  the  engineer. 

Before  investigating  present  methods  and  future  prob- 
abilities it  will  be  profitable  to  examine  earlier  systems, 
with  their  weak  points  and  causes  of  failure. 

The  oldest  so-called  fire-proof  arches  consisted  of  I 
beams,  placed  about  5  feet  centres,  with  4-inch  brick  arches 
turned  between,  then  levelled  up  with  concrete  containing 
the  nailing-strips  for  the  wooden  flooring.  Corrugated 
iron,  sprung  from  flange  to  flange,  was  also  used  in  place 
of  the  brickwork,  and  this  latter  type  may  still  be  seen  in 
some  of  the  more  substantial  buildings  oi  that  epoch,  which 

54 


FLOORS  AND  FLOOR  FRAMLNG.  55 

have  survived  to  the  present  time.  This  construction  was 
decidedly  faulty,  however,  not  alone  in  the  weakness  of  the 
arch  itself  under  the  action  of  fire,  but  in  the  fact  that  the 
lower  flanges  of  the  supporting-  I  beams,  and  the  entire  cast 
columns  then  in  use,  were  left  exposed  to  view,  and,  what 
was  much  more  serious,  to  the  possibility  of  contact  with  fire. 

This  unsatisfactory  and  weighty  construction,  shown  in 
Figs.  22  and  23,  gave  way,  as  has  been  said,  to  the  superior 


Fig.  23. 

advantages  of  terra-cotta  or  tile — superior  in  fire-resisting 
qualities,  as  well  as  in  greater  lightness. 

Hollow  tile  is  made  from  fire-clay,  moulded  by  dies  into 
the  various  hollow  forms  required  for  commercial  use. 
The  clay  is  subjected  during  its  manufacture  to  a  high 
pressure  while  in  a  moist  or  damp  state,  which  accounts 
for  its  great  strength,  and  after  drying  is  burned,  like  terra- 
cotta, in  a  kiln. 


Fig.  24. 

The  clay  used  in  the  manufacture  of  fire-proofing  ma- 
terial must  be  of  a  refractory  nature — as  plastic  fire-clay, 
semi-fire-clay,  or  fire-clay  mixed  with  plastic  clay  or  shale. 
But  few  clays  have  been  found  that  are  practicable  of 


56  ARCHITECTURAL  ENGINEERING. 

manufacture  into  a  floor  of  the  required  strength,  and  relia- 
bility against  fire. 

TILE  ARCHES. 

The  earlier  forms  of  tile  arches  were  made  as  in  Fig.  24, 
which  shows  the  arch  used  in  the  Equitable  Building  in 
Chicago  (1872),  and  Fig.  25,  which  shows  tile  arch  in  the 


i 


Fig.  25. 

Montauk  Building,  Chicago  (1 88 1).  The  latter  may  be  said 
to  have  been  the  first  building  of  modern  design  in  Chicago. 
The  arches  were  6  inches  deep,  with  a  span  of  3  to  4  feet. 
But  as  these  forms  still  left  the  lower  flanges  of  the  I  beams 
unprotected,  they  were  soon  superseded  by  the  type  shown 


Fig.  26. 

in  Fig.  26.  This  arch  was  used  in  the  Home  Insurance 
Building,  Chicago  (1884),  the  tile  being  9  inches  deep  and 
6  foot  span.  This  was  the  first  instance  in  which  the  beam 
soffits  were  protected  against  fire  by  anything  more  than 
plaster ;  and  as  many  of  the  features  in  this  arch  are  essen- 
tially the  same  as  in  the  types  of  tile  arches  as  found  in 
present  practice,  a  brief  description  will  here  be  in  place. 

The  pieces  form  radial  joints,  as  in  any  segmental  arch, 
or  are  key-shaped  with  a  centre  "  key."  The  arches  are  set 
on  *'  centres  "  of  plank,  hung  from  the  beams  by  hook-bolts, 
and  these  centres  should  remain  in  place  at  least  twenty- 


FLOORS  AND  FLOOR  FRAMING. 


57 


four  hours  after  the  arches  are  set.  The  "  skew-backs," 
or  butment  pieces  of  the  arch,  take  the  shape  of  the  I  beam 
against  which  they  bear,  setting  firmly  and  squarely  on  the 
beam  flanges.  Different  sized  skew-backs  are  at  hand  for 
use  with  different  sized  beams,  as  arches  are  often  sprung 
between  beams  of  different  depths.  The  soffit  of  the  tile 
arch  extends  about  one  inch  below  the  bottoms  of  the  beams, 
and  the  skew-back  pieces  are  made  in  such  a  manner  that 
a  piece  of  fire-proofing  tile  may  be  slipped  in  and  sup. 
ported  directly  underneath  the  beam  flange,  to  complete 
the  fire-proofing,  as  shown  in  Fig.  26.  A  coat  of  plaster 
or  cement  is  then  given  the  whole  surface,  after  which  it 
is  ready  for  such  decorative  treatment  as  may  be  desired. 

A  concrete  filling  is  placed  over  the  arch,  to  distribute 
the  load  from  block  to  block,  and  to  receive  and  embed 
the  wooden  nailing-strips  which  take  the  finished  flooring. 
The  metal  beams  are  thus  entirely  surrounded  by  fire-clay, 
concrete,  and  cement. 

The  depth  of  the  tile  arch  depends  upon  the  span,  and 
the  load  to  be  carried.    The  maximum  spans  of  the  various 


depths  are  generally  furnished  by  the  manufacturer  of  the 
type  in  question,  but  such  data  should  be  fully  established 
by  adequate  tests,  as  will  be  pointed  out  later.  Slight 
variations  in  the  span  from  centre  to  centre  of  beams  are 
made  by  using  u  half  intermediate  "  tile,  and  different-sized 
keys.    The  tile  blocks  are  laid  with  lime  mortar  or  cement 


!    SPPIWPF  '  CONCRETE" 


2.0 


Fig.  27. 


5S 


ARCHITECTURAL  ENGINEERING. 


joints,  and  in  no  case  should  the  joint  exceed  -J  inch  in 
thickness. 

In  many  cases,  where  the  panel  length  required  beams 
of  a  considerably  greater  depth  than  the  tile  arch  itself, 
tile  filling-blocks  were  used,  as  being  lighter  than  the 
ordinary  concrete  filling — as  shown  in  Fig.  27,  taken  from 
the  Woman's  Temple,  Chicago.  Special  shapes  for  skew- 
backs,  panelled  beams,  etc.,  made  in  this  character  of  tile, 
are  shown  in  Figs.  28  and  29. 


The  best  semi-porous  tile  used  in  these  types  was  made 
from  clay  found  at  Chaska,  Minn.,  at  Brazil,  Ind.,  and  in 
parts  of  eastern  New  Jersey. 

In  the  foregoing  examples  of  arches,  known  generally 
as  the  "Pioneer"  arches  (because  made  by  the  Pioneer 
Fire-proofing  Company  of  Chicago),  the  voids  in  the  tile 
blocks  ran  parallel  to  the  supporting  beams,  and  hence  the 
principal  or  side  webs  of  the  individual  tile  blocks  also 
ran  parallel  to  the  beams,  or  at  right  angles  to  the  line  of 
thrust  in  the  arch.  This  limited  the  effective  arch  area  to 
the  top  and  bottom  flanges,  involving  a  serious  waste  of 
material. 

To  remedy  this  defect  a  new  arch  was  patented 
a  lew  years  ago,  known  as  the  "  Lee  "  arch,  in  which 
the  voids  ran  parallel  to  the  line  of  thrust,  or  at  right 
angles  to  the  supporting  beams.  One  of  these  arches  is 
shown  in  Fig.  30,  and  it  will  be  seen  that  the  effective 
area  now  comprises  the  vertical  webs,  as  well  as  the  hori- 
zontal ribs;  in  other  words,  all  of  the  material  performs 
useful  work  as  an  arch.  A  further  improvement  was 
attempted  by  the  use  of  a  porous  terra-cotta,  made  from 


Fig.  28. 


Fig.  29. 


I 


FLOORS  AND  FLOOR  FRAMLNG.  59» 

a  fire-clay  which,  before  it  is  burned,  is  mixed  with  saw- 
dust and  finely  cut  straw.  These  ingredients  are  con- 
sumed during  the  firing,  leaving  the  material  in  a  very 
porous   condition,  and   thus  greatly  reducing   the  dead 


Fig.  30. 

weight  of  the  arch  itself.  A  comparison  of  the  weights  of 
the  old  Pioneer  and  the  newer  Lee  arch  may  be  made  as 
follows  (weight  given  is  per  square  foot) : 

Pioneer.  Lee. 

9"  arch   33  lbs.  25  lbs. 

10"     "    37   "  30  " 

12"     "    40   "  35  " 

15"     "   40  " 

Another  step  of  progress  lay  in  the  skew-back  or  but- 
ment  pieces,  which  gave  a  better  bearing  against  the  beam 
webs  by  means  of  intermediate  cross-ribs,  as  well  as  by  the 
top  and  bottom  flanges. 

Some  very  interesting  and  valuable  tests  of  fire-proof 
floor  arches  built  after  the  Pioneer  and  Lee  methods  were 
published  in  No.  796  of  the  American  Architect  and  Build- 
ing News — undoubtedly  forming  one  of  the  most  satisfac- 
tory and  extensive  series  of  public  tests  yet  attempted  on 
such  construction.  The  trials  were  made  in  Denver,  Col., 
1892,  for  the  Denver  Equitable  Building  Company,  under 
the  supervision  of  a  board  of  architects.  The  arches  were 
sprung  from  beams  placed  5  ft.  centres,  as  shown  in  Fig.  30, 
and  the  conditions  included  static  loading,  a  drop  test,  a 
fire  and  water  test,  and  a  continuous  fire  test. 

In  the  test  for  static  loads  the  Lee  arch  deflected  grad- 


6o 


ARCHITECTURAL  ENGINEERING. 


ually  under  the  increased  weights  to  .065  of  a  foot,  sustain- 
ing a  final  load  of  15,145  lbs.  for  two  hours.  The  Pioneer 
arch  gave  way  suddenly  at  the  haunches  under  a  load  of 
5,429  lbs. 

In  the  drop  test  a  piece  of  wood  12"  X  12"  X  4'  was 
let  fall  from  a  height  of  6'  o".  The  Pioneer  arch  was  shat- 
tered at  the  first  blow,  while  the  Lee  arch,  under  the  same 
test,  stood  up  to  the  eleventh  drop,  the  former  blows  shat- 
tering but  parts  of  the  arch. 

In  the  fire  and  water  tests,  three  applications  of  water 

combined  with  fire  destroyed  the  Pioneer  arch,  while  the 

Lee  arch  received  eleven  applications  of  water,  and  at  the 

end  of  twenty-three  hours  remained  practically  uninjured, 

requiring  eleven  blows  from  the  ram  to  break  it. 

In  the  continuous  fire  test  the  fire  was  maintained  con- 

» 

tinuously  beneath  a  Lee  arch  for  twenty-four  hours,  and 
the  arch  then  supported  a  load  of  bricks  of  12,500  lbs.  on 
a  space  3'  o"  wide  in  the  central  portion  of  the  arch. 

Considering  the  static  loads,  the  results  may  be  better 
judged  as  follows  : 


This  certainly  shows  a  great  step  of  advancement  for 
the  Lee  arch,  but,  assuming  a  factor  of  safety  of  8,  as 
recommended  by  Rankine,  and  a  total  load  of  165  lbs.  per 
square  foot  (85  lbs.  dead  -f-  80  lbs.  live),  a  uniform  break- 
ing-load of  1320  lbs.  per  square  foot  is  needed  before  the 
tile  arch  can  be  considered  fully  acceptable. 

Tests  of  the  12"  blocks  of  the  Empire  Fire-proofing 
Company  might  also  be  mentioned,  made  in  1891  by  the 
city  engineer  of  Richmond,  Va.    A  variation  in  the  break- 


Pioneer. 


Lee. 


Breaking-load  per  square  foot  of  9  sq.  ft.  loaded  area. 
Reduced  to  equally  distributed  load,  3'  o"  X  5'  o '  .... 
Assumed  load  per  square  foot,  as  occurring  in  practice 
Coefficient  of  safety  


lbs. 
603 
360 
150 


lbs. 
1670 
1008 

I50 


FLOORS  AND  FLOOR  FRAMLNG.  6 1 

ing-load  was  recorded  of  from  554  to  1057  lbs.  per  square 
foot.  But  it  must  be  remembered  that  too  much  impor- 
tance must  not  be  placed  on  these  maximum  figures.  The 
average  breaking-loads  of  such  tests  must  be  considered  a 
fair  figure  at  which  to  judge  the  general  run  of  arches  as 
placed  in  actual  use  by  these  companies;  and  in  this  light 
the  room  and  actual  necessity  for  still  further  improve- 
ment becomes  self-evident. 

A  still  later  patent  known  as  "  Johnson's  patent  flat 
arch,"  (see  Fig.  31),  is  the  one  used  most  extensively  in  the 

 7*>l  , 

ii.4-— 

-  —  *p  1 — 

2 

Fig.  31. 

buildings  of  late  erection.  It  is  made  of  hard  terra  cotta 
with  thinner  webs  than  were  formerly  employed,  and  is  of 
the  "  end  construction,"  thus  utilizing  all  of  the  material  as 
in  the  Lee  arch.  This  type  seemed  to  meet  with  much 
favor  at  first,  and  it  was  used  in  quite  a  number  of 
Chicago's  best  buildings,  but  experience  would  seem  to 
point  to  the  porous  tile  as  being  far  more  satisfactory  in 
its  fire-resisting  qualities  than  the  hard  tile.  A  test:  by 
fire  and  water  of  a  wall  of  hard  tile  blocks  occurred  some 
time  ago  in  the  rear  of  the  Schiller  Theatre  Building, 
Chicago.  The  combined  action  of  heat  and  cold  water 
caused  the  blocks  to  crack  to  such  an  extent  that  they  soon 
fell  from  the  metal  uprights  in  considerable  areas. 

Soft  tile  or  porous  terra-cotta  has  been  specified  for  all 
fire-proofing  work  in  the  latest  buildings  designed  by  Mr. 
W.  L.  B.  Jenney,  notably  the  New  York  Life  Insurance 
and  the  Fort  Dearborn  buildings. 


62 


ARCHITECTURAL  ENGINEERING. 


Tie-rods  are  necessary  in  all  these  forms  of  arches,  to 
take  up  the  horizontal  thrusts  without  dependence  on  the 
adjoining  arches.  Such  rods  are  generally  f  inch  diameter, 
and  spaced  from  5  to  7  feet  apart.  All  tests  of  tile  arches 
should  require  the  tie-rods  to  be  without  initial  strain  ;  for 
if  the  rods  be  screwed  up  sufficiently  to  give  an  initial 
strain  equal  to  the  tensile  strength  of  the  tile  or  cement- 
ing material  between  the  blocks,  then  is  the  tensile 
strength  of  the  arch  for  the  breaking-load  reduced  to  o, 
and  the  beam  may  be  reloaded  to  the  same  amount. 

Reference  to  the  Appendix  table  giving  the  principal 
points  of  construction  in  the  notable  office  buildings  in 
Chicago  will  show  that  either  the  "  Pioneer,"  "  Lee,"  or 
"Johnson's"  type  of  floor  arch  is  used  in  nearly  every 
case,  although  it  must  be  admitted  that  such  a  general  use 
of  tile  construction  is  far  from  being  a  guarantee  of  its  per- 
fection. Indeed,  it  is.no  exaggeration  to  say  that  there  is 
scarcely  a  single  material  used  in  constructional  work  in 
regard  to  which  we  have  as  limited  a  knowledge  of  its 
general  or  specific  properties  of  resistance  as  is  found  in 
terra-cotta  or  tilework  ;  and  yet,  in  the  modern  building 
the  use  of  this  style  of  floor  has  become  so  widely  ex- 
tended that  terra-cotta  or  hollow  tile  has  become  one  of  the 
most  ordinary  materials  of  construction.  Its  functions  are 
no  less  positive  than  those  of  the  structural  steelwork  or 
masonry-work,  forming,  as  it  does,  the  supporting  area  for 
all  dead  and  live  loads  coming  on  the  floor  system — crowds 
in  halls,  theatres,  and  other  places  of  public  gathering,  as 
well  as  small  safes,  desks,  and  the  many  articles  forming 
concentrated  loads. 

Any  failure  in  the  hollow  tile  would  be  apt  to  result 
in  quite  as  great  disaster  or  loss  of  life  and  limb  as  would 
proceed  from  any  failure  in  the  iron  or  steel  skeleton.  It 
is  apparent,  therefore,  that  the  sustaining  power  of  hoi- 


FLOORS  AND  FLOOR  FRAMLNG.  63 

low-tile  work  should  be  absolutely  definite,  and  that  its  use 
should  be  governed  by  well-defined  tests,  or  rules  based 
on  such  tests. 

Some  attempts  on  the  part  of  the  writer  to  secure  reli- 
able facts  pertaining  to  tests  on  some  of  the  newer  tile 
floor  arches  in  almost  daily  use,  developed  the  fact  that 
the  fire-proofing  companies  had  no  data  "  in  shape  to  be 
made  public,"  although  the  very  types  of  arches  about 
which  information  was  asked,  had  already  been  used  in  a 
number  of  prominent  buildings.  This  leads  to  the  opinion 
that  architects  and  owners  are  too  free  in  accepting  the 
alleged  results  of  tests,  or  in  accepting  some  general  style 
of  arch  because  it  has  been  used  elsewhere.  When  iron 
and  steel  specifications  require  severe  tests  from  the  fin- 
ished material,  representing  each  blow  or  cast,  it  would 
hardly  seem  more  unreasonable  to  require  actual  tests  for 
the  style  of  arch  used  before  accepting  such  arches  for  any 
particular  building.  It  is  only  by  such  repeated  tests,  and 
competition  based  on  actual  results  in  each  instance,  that 
the  most  economical  designs  for  floors  can  be  obtained, 
consistent  with  good  engineering  principles ;  and  it  is  cer- 
tain that  such  tests  and  open  competitions  would  lead  to 
better  quality,  if  not  to  better  forms  and  details.  Both 
concentrated  and  uniform  loads  should  be  considered,  as 
occurring  in  actual  circumstances. 

The  most  satisfactory  set  of  public  tests  on  tile  arches, 
in  which  quality  and  not  price  has  determined  the  award 
of  the  contract,  were  those  made  for  the  Equitable  Life  In- 
surance Building  in  Denver,  Col.,  already  referred  to.  A 
load  of  1008  lbs.  per  square  foot  equally  distributed  was 
carried  in  this  instance,  and  though  even  higher  figures  are 
claimed  for  later  patent  arches,  the  prime  consideration  of 
price  in  the  usual  letting  of  contracts  will  soon  tempt  the 
less  reliable  fire-proofing  companies  either  to  juggle  their 


64 


ARCHITECTURAL  ENGINEERING. 


figures  into  deceiving  records  of  tests,  as  is  often  done,  or 
to  furnish  poorer  and  poorer  material  as  competition  in- 
creases and  searching  inquiry  decreases. 

Rankine  advises  the  use  of  \  to  \  the  ultimate  strength 
in  metals,  \  to  XV  in  wood,  and  £  to  \  in  masonry.  Consider- 
ing hollow  tile  as  coming  under  the  head  of  the  poorest 
class  of  masonry,  an  ultimate  strength  should  therefore  be 
required  of  eight  times  the  allowable  stress,  if  it  is  wished 
to  procure  uniform  safety  in  a  floor  of  steel  beams  and  tile 
arches.  Assuming  an  arch  carrying  a  live  load  of  80  lbs. 
per  square  foot,  a  dead  load  of  85  lbs.  per  square  foot  (or  165 
lbs.  total),  the  manufacturer  should  be  required  to  show  by 
tests  on  the  site  that  the  type  submitted  is  able  safely  to 
stand  a  load  of  1320  lbs.  per  square  foot,  and  this  before 
being  allowed  to  compete  in  the  question  of  cost.  The 
writer  is  aware  of  the  objections  of  time  and  cost  to  such 
methods,  but  in  this  way  only  can  the  excellence  be  main- 
tained, and  assurance  be  provided  that  the  floor  arch  is 
what  it  should  be. 

The  unusual  interest  which  is  being  displayed  in  the 
subject  of  fire-proof  floors,  of  tile  and  other  materials,  is 
evidenced  by  the  series  of  articles  but  lately  begun  in  a 
periodical  devoted  to  the  interests  of  the  clay  products. 
This  series  of  articles  contemplates  a  complete  record,  as 
far  as  possible,  of  all  tests  on  fire-proof  arches  of  ordinary 
patterns,  up  to  present  date,  with  comments  011  the  causes 
of  failure  and  possibilities  of  improvement.  Such  work 
cannot  fail  to  be  productive  of  the  most  beneficial  results. 

The  writer  believes  that  the  section  devoted  to  the  arch- 
like action  in  present  tile  floors  is  still  too  small.  This  is 
indicated  by  the  sudden  collapse  of  many  arches  at  the 
haunches  while  under  test.  It  would  also  seem,  through 
past  tests,  that  too  much  reliance  has  been  placed  in  the 
use  of  strong  cementing  materials  between  the  blocks,  thus 


FLOORS  AND  FLOOR  FRAMING.  65 

making  the  arch  act  as  a  monolithic  piece.  Hollow  tile 
blocks,  as  used  in  present  forms  of  arches,  cannot  be  con- 
sidered as  a  beam,  even  with  the  best  of  cement  joints. 
They  must  still  form  a  flat  arch,  whose  line  of  resistance 
must  be  determined  precisely  the  same  as  in  any  segmental 
arch.  The  fact  that  the  arch  blocks  are  of  a  uniform  depth 
cannot  in  any  way  change  the  mechanical  conditions  under 
which  the  loads  and  supporting  forces  act. 

Present  types  of  tile  arches  do  not  admit  of  a  proper 
calculation  of  their  dimensions  according  to  the  loads  for 
which  they  are  designed  ;  the  horizontal  bearing-ribs  are 
still  relied  upon  to  help  make  up  the  required  section,  and 
the  height  of  the  section  as  well  as  the  thickness  of  the 
tile  webs,  under  different  spans  and  loads,  is  left  entirely 
to  the  option  of  the  manufacturer.  None  of  the  building 
laws  prescribe  any  conditions  for  the  proper  calculation  of 
floor  arches  under  varying  spans  and  loads,  except  to 
define  a  minimum  depth  of  arch  blocks. 

The  depth  of  the  tile  arch  should  be  nearly  equal  to  the 
depth  of  the  supporting  I  beams,  in  order  to  secure  the 
most  economical  results,  for  this  arrangement  will  be  the 
cheapest  in  the  cost  of  the  floor  per  square  foot,  consider- 
ing tile  and  concrete  filling,  and  the  lightest,  considering 
the  dead  load. 

An  arch  has  been  patented  as  shown  in  Fig.  32,  but  it  is 
evident  that  the  concrete  or  cinder  filling  at  the  haunches 


Fig.  32. 


will  cause  the  arch  to  weigh  more  than  if  the  tile  blocks 
extended  up  to  the  tops  of  the  beams ;  while  the  mere  fact 


66 


ARCHITECTURAL  ENGINEERING. 


of  the  arch  being  made  with  a  segmental  top  adds  nothing 
to  the  strength. 

CONCRETE  ARCHES. 

As  has  been  stated  before,  the  widespread  interest  dis- 
played in  the  subject  of  fire-proof  floors  is  indicated  by  the 
numerous  types  which  have  entered  the  field  in  competi- 
tion with  the  hollow-tile  flooring.  It  is  certainly  no  diffi- 
cult problem  to  design  and  construct  a  floor  which  will  be 
of  sufficient  strength  and  of  satisfactory  fire-resisting  proper- 
ties out  of  fire-clay,  cement,  or  concrete.  But  when  the 
elements  of  minimum  cost  and  minimum  weight  must  be 
considered  with  maximum  efficiency,  the  solution  is  not  so 
apparent. 

Up  to  the  present  day  fire-proof  floors  have  been  enor- 
mously heavy,  consisting  largely  of  dead  weight  in  the 
most  literal  sense  of  the  word.  Such  wTeights  add  greatly 
to  the  cost  of  a  building,  and  yet  serve  to  little  or  no  pur- 
pose in  strengthening  or  stiffening  the  structure.  Hence 
the  endeavor  to  provide  a  substitute  for  the  hollow-tile 
floor  which  shall  yield  an  increase  in  unit  strength,  and 
thus  decrease  the  dead  weight  and  consequent  cost. 

A  variety  of  combinations  of  iron  or  steel  and  concrete 
as  applied  to  floorings  has  lately  been  employed,  and 
would  seem  to  possess  features  of  great  merit  and  of  wide- 
spread application.  Floors  constructed  of  concrete  and 
steel,  with  the  latter  thoroughly  protected  against  corro- 
sion, would  certainly  possess  the  great  advantages  of  in- 
combustibility and  durability.  It  has  long  been  claimed 
that  the  unequal  rates  of  expansion  and  contraction  of  iron 
and  concrete  or  cement  under  thermic  changes  would  soon 
destroy  such  a  combination,  but  experiments  have  been 
made  which  show  that  these  rates  are  so  nearly  the  same 
that  they  may  properly  be  considered  identical.    The  re- 


FLOORS  AND  FLOOR  FRAMING. 


67 


cent  tests  of  such  flooring  at  Trenton,  N.  J.  (see  Engineering 
Record,  December  22,  1894),  would  also  seem  to  point  to 
the  successful  fire  endurance  of  such  combinations. 

The  weakest  points  against  fire  would  appear  to  be  the 
thin  coating  of  cement  plaster  directly  underneath  the 
beam  flanges,  where  a  stream  of  cold  water  applied  to  the 
highly  heated  cement  would  probably  cause  it  to  crack  off, 
and  leave  the  metal-work  exposed. 

It  is  of  great  importance  to  ascertain  these  points  by 
means  of  actual  tests  before  final  adoption,  the  same  as 
in  the  case  of  tile  arches  ;  while  the  most  judicious  form  of 
the  metal-work,  and  the  shape  and  character  of  the  moulded 
concrete  to  develop  the  maximum  resistance  with  the  least 
weight,  must  also  be  determined  by  repeated  tests. 

The  different  character  of  the  metal-work  in  combina- 
tion with  the  concrete,  presents  three  varieties :  floors 
using  curved  I  beams,  those  using  steel  straps,  and  those 
using  wires. 

1.  Curved  I  Beams. — This  system,  shown  in  Figs.  33  and 
34,  is  called  the  Melan  system,  from  the  inventor,  J.  Melan, 


who  has  constructed  many  bridges  of  this  type  in  Europe. 
It  consists  of  bent  I  beams,  spaced  about  5  ft.  centres,  with 


Fig.  33. 


Fig.  34. 


68 


ARCHITECTURAL  ENGINEERING. 


concrete  body  or  slabs  between.  A  filling  of  cinders  or 
other  light  material  is  then  used  to  level  up  the  surface 
and  receive  the  nailing-strips,  as  in  other  floors.  A  great 
saving  in  dead  weight  and  cost  is  claimed  for  this  system, 
but  it  still  possesses  great  disadvantages  which,  in  the 
opinion  of  the  writer,  will  seriously  restrict  its  use. 

The  concrete  must  perforin  a  twofold  duty.  It  helps 
to  take  up  the  compression  of  the  arch,  and  at  the  same 
time  must  act  as  a  beam  between  the  curved  ribs.  The 
fibres  are  then  brought  under  maximum  strain  in  two  direc- 
tions, and  if  we  adhere  to  the  usage  of  allowing  no  cement 
in  tension,  this  combination  becomes  poor  engineering 
practice. 

In  most  cases  where  appearances  are  considered,  a  sus- 
pended ceiling  will  be  necessary.  Tenants  and  owners 
desire  a  ceiling  of  unbroken  plane,  for  the  sake  of  light  as 
well  as  appearance.  If  such  a  suspended  ceiling  is  to  be  of 
fire-proof  construction,  it  will  necessarily  add  materially  to- 
the  weight  and  cost ;  or,  if  it  is  not  of  fire-proof  material,  a 
large  amount  of  combustible  material  is  added  in  a  very 
dangerous  position. 

Exposed  tie-rods  are  necessary,  unless  a  suspended  ceil- 
ing be  used. 

The  workmanship  must  be  of  the  most  careful  charac- 
ter, to  insure  the  proper  results  from  these  concrete  beams. 

2.  Concrete  and  Steel  Straps. — Concrete  floors  in  com- 
bination with  steel  straps  have  been  used  in  the  follow- 
ing buildings :  Drexel  Institute,  American  Philosophical 
Society  Building,  and  Academy  of  Natural  Sciences,  in 
Philadelphia,  and  in  the  Alumni  Building  of  Rensselaer 
Polytechnic  Institute  at  Troy.  This  form  of  flooring, 
shown  in  Fig.  35,  consists  of  I-beam  girders  spaced 
8'  o"  to  18'  o"  centres  as  may  be  required,  between 
which  are  hung  steel  straps  at  intervals  of  from  12"  to  24", 


FLOORS  AND  FLOOR  FRAMING. 


69 


with  their  ends  bent  or  hooked  over  the  top  flanges  of  the 
girders.  The  straps  curve  downward,  and  midway  in  their 
length   hang  close   to  the    ceiling-line.     A  concrete  or 


/PART  CEMENT  \ 
'  6 AND. 


Fig.  35. 

cement  filling  is  used,  embedding  the  straps  and  girders. 
If  the  beams  are  of  considerable  depth,  the  soffit  of  the 
arch  may  show  the  panelled  beams,  as  in  Fig.  36.  The 


HOOK 


mm 


5  G^SPIPE 
WIRE:  NETTING 


Fig.  36. 

upper  layer  of  cement  may  be  laid  in  colored  geometrical 
patterns,  or,  if  a  wood  floor  is  used,  this  upper  layer  of  cement 
is  made  but  1"  in  thickness,  with  nailing-strips  embedded. 

The  following  table  gives  data  from  two  of  the  build- 
ings before  mentioned  : 


Building. 

Span. 

Straps. 

Centre  to 

Centre 
of  Straps. 

Thickness 
of 

Concrete. 

Assumed  Load. 

American  Philosophical) 
Academy  Natural  Sciences 

8' 
16' 
16' 
18' 

3"  v  8" 

2i"  X  f" 
2  "  X  f" 

4"  x  r 

24" 
24" 
12" 
18" 

4" 
7" 
8" 
8" 

80  lbs.  live  load. 

80  "      "  " 
210   "  total  " 
100  "  live  " 

3.  Concrete  Floors  with  Twisted  Wires  or  Rods  (see  Fig.  36). 
— This  method  is  very  similar  to  the  previous  type,  except 
that  wires  are  used  instead  of  straps.  The  wires  are 
secured  to  the  beams  by  means  of  hooks,  3"  Ion 


g,  made  of 


70  ARCHITECTURAL  ENGINEERING. 

\"  square  iron.  The  wires  are  of  twisted  double  strand, 
No.  12  gauge,  with  a  length  of  gas-pipe  laid  on  them  at  the 
centre  of  the  span  to  give  them  a  uniform  sag.  The  filling 
consists  of  five  parts  by  weight  of  plaster  of  Paris,  and  one 
part  of  wood  shavings,  mixed  with  sufficient  water  to  bring 
the  mass  to  the  consistency  of  a  thin  paste.  This  filling  is 
laid  on  a  level  centering,  as  in  the  previous  type.  The  dis- 
tance between  the  wires  is  varied,  according  to  the  load 
to  be  provided  for. 

Where  a  flat  ceiling  surface  is  desired,  this  type  is  modi- 
fied, as  shown  in  Fig.  37.    The  floor-plate  is  constructed  on 


! 


Fig.  37. 

wires  as  before,  while  the  ceiling-plate  is  made  of  the  same 
composition,  but  with  flat  bars  embedded  therein,  resting 
on  the  lower  flanges  of  the  I  beams. 

Tests  of  this  flooring  under  static  loads  have  been  made 
as  follows : 


Distance 
between 

Beams, 
Centre  to 

Centre. 

Clear 
Span  be- 
tween 
Flanges. 

Length 

of 
Section 
Tested. 

Area 
Tested, 
Square 

Feet. 

Total 
Load  in 
Lbs. 

Load 
per 
Sq.  Ft. 
in  Lbs. 

Remarks. 

4'  7" 

4'  2" 

i'  0" 

4.166 

5,630 

1,351 

Did  not  fail.   Test  made 

in  building  under  con- 
tract. 

5'  5" 

5'  O" 

0'  9f 

3-958 

7,600 

1,920 

Two  cables  on  one  side 
broke,     others    u  n  - 
broken. 

4'  6" 

4'  of 

2'  6" 

IO.IO5 

15,682 

1. 551 

Failed  by  breaking  of 

cables  on  one  side. 

4' 6" 

4'  of 

5'  of 

20.38 

29.3M 

1,438 

Adjoining  sections,  be- 
ing without  load, lifted. 
No  wires  broken. 

FLOORS  AND  FLOOR  FRAMING. 


The  fire  and  water  tests  also  proved  very  satisfactory  ; 
indeed,  plaster  of  Paris  or  gypsum  has  been  used  in  Europe 
for  many  years  as  a  fire-proof  material. 

The  greatest  objections  to  these  arches  lie  in  the  dis- 
coloration of  the  plastered  ceiling,  due  to  the  rusting  of 
the  wires,  and  the  excessive  amount  of  water  retained  for  a 
long  time  by  the  sawdust.  Galvanized  wires  should  be 
used,  and  some  material  substituted  for  the  sawdust. 

Another  form  of  concrete  arch  which  has  been  used  in 
California  (see  Engineering  Record,  March  24,  1894)  depends 


Fig.  38. 


on  twisted  iron  rods  i\"  X  i\"  for  support  (see  Fig.  38). 
The  concrete  arches  are  f  4"  centre  to  centre  of  columns 
without  the  aid  of  any  metal-work.  The  columns  are 
placed  25/o//  centres  longitudinally,  with  4  twisted  rods  act- 
ing as  supports  between.  The  concrete  slabs  are  joined  by 
-a  lap  joint,  with  a  lead  strip  embedded  to  prevent  the  pas- 
sage of  water.  This  type  was  tested  to  300  lbs.  per  square 
foot.  The  arches  deflected  \"  at  the  centre  and  remained 
uninjured.  Such  construction  is  hardly  applicable  to  office 
buildings  on  account  of  the  curved  soffit,  and  small  trans- 
verse space  between  columns,  but  modifications  of  this 
form  would  seem  to  offer  many  advantages  in  roof  con- 
struction. 


72 


ARCHITECTURAL  ENGINEERING. 


SEGMENTAL  ARCHES  OF  TILE. 

For  long  spans  in  buildings  where  a  flat  ceiling  is  not 
necessary,  as  in  warehouses,  etc.,  a  segmental  arch  is  often 
used,  following  the  curve  of  pressure,  as  shown  in  Fig.  39. 


Fig.  39. 

The  tie-rods,  spaced  equally,  are  encased  in  tile  to  give  a 
panelled  effect.    The  arch  shown  in  Fig.  40  was  used  with 


Fig.  40. 

extra  heavy  tiles  in  the  Sibley  Warehouse,  Chicago.*  The 
use  of  such  segmental  arches  for  office  buildings  has  been 
abandoned  after  a  trial  in  the  Rand-McNally  Building, 
Chicago.  A  ceiling  of  flat  tile  was  there  suspended  under 
a  segmental  arch,  but  it  did  not  prove  successful,  and  has 
not  since  been  used. 

The  floor  of  N.  Poulson  also  deserves  special  notice, 
but  the  use  of  these  particular  arches  seems  somewhat 
limited  up  to  the  present  time  to  public  buildings,  libraries, 
etc.,  where  the  groined  arch  is  more  suitable  than  in  office 
structures.  There  is  no  example  of  the  Poulson  arch  in 
Chicago,  to  the  writer's  knowledge.  The  system  may  be 
described  as  follows  :  The  total  floor-space  is  divided  into 
panels  of  about  25'  each  way  by  the  columns,  with  con- 

*  Tests  at  Washington,  D.  C,  March  26,  1894,  on  a  segmental  arch  15'  4" 
span,  y1^"  rise,  and  using  blocks  8"  at  the  haunches  and  6"  at  the  centre,  de- 
veloped a  safe  capacity  of  iooo  lbs.  per  square  foot  of  bearing  surface. 


FLO  OAS  AND  FLOOR  FRAMLNG .  73 

necting  lattice  girders.  These  panels  are  spanned  by  a 
system  of  arched  flats,  generally  3"X  i  ",  with  a  rise  of 
1 8".  The  thrust  of  the  arches  is  taken  up  by  an  octagonal 
frame  of  angle  irons  in  each  panel.  All  arch  intersections 
are  bolted.  These  flats  are  built  into  the  lower  parts  of 
concrete  beams,  which  carry  the  floor  on  their  upper 
edges,  and  curved  plaster  soffits  on  the  under  sides,  form- 
ing the  ceiling  ribs.  A  rubber  bag,  held  up  by  an  umbrella 
scaffold,  is  pressed  up  into  the  triangular  space  formed  by 
the  intersecting  ribs,  and  a  plaster  of  Paris  or  cement  soffit 
is  formed  with  the  curved  bag  for  support.  Heavy  steel 
wires  are  then  stretched  over  the  system,  which  wires,  in 
turn,  support  galvanized  wire  cloth.  A  3"  cement  filling  is 
then  placed  on  top  to  hold  the  nailing-strips. 

"  CUASTAVINO  "  ARCH. 
The  peculiar  strength  of  the  egg-shell,  or  of  any  con- 
tinuous layer  of  material,  flat,  curved,  or  dished,  like  the 
buckle-plate  for  example,  undoubtedly  suggested  the  form 
of  the  Guastavino  arch.  Arch  or  dome  shells  are  built  of 
small  rectangular  tiles  of  hard  terra-cotta,  three  or  four 
layers  being  used,  of  \"  thickness  each,  laid  together  in 
either  square  or  herring-bone  bond.  Portland  cement  is 
used  for  the  joints  and  between  the  concentric  layers  or 
shells.  The  great  strength  of  these  arches  lies  in  the  fact 
that  they  follow  closely  the  curve  of  pressure,  thus  avoid- 
ing tension  in  the  voussoirs,  and  in  the  fact  that  the  suc- 
cessive layers  break  joint  so  perfectly  that  to  open  any 
joint  several  tiles  must  be  sheared  off.  The  great  dis- 
advantage in  the  use  of  this  type  in  mercantile  or  office 
buildings  lies  in  the  curved  soffit,  and  the  necessary  use 
of  exposed  tie-rods  where  several  spans  occur  side  by  side. 
In  solid  masonry  construction,  as  in  libraries,  public  build- 
ings, etc.,  where  the  walls  or  piers  are  capable  of  resisting 


74 


ARCHITECTURAL  ENGINEERING. 


the  horizontal  thrusts,  and  where  a  curved  soffit  is  in 
keeping,  this  type  possesses  great  advantages. 

It  will  be  noticed  that  little  has  been  said  as  regards 
the  comparative  cost  of  the  types  of  flooring  here  men- 
tioned. This  question  will  undoubtedly  serve  as  a  prime 
factor  in  making  a  choice  between  the  various  methods, 
but,  as  stated  before,  the  question  of  expense  should  be 
held  entirely  subservient  to  that  of  safety,  both  present  and 
future.  Two  different  types  of  floor  construction,  with  a 
considerable  variance  in  the  ultimate  capacity,  cannot  prop- 
erly be  compared  in  the  question  of  cost.  If  all  methods 
meet  the  maximum  requirements,  the  conditions  are  equal, 
and  the  cost  may  be  considered  as  the  determining  factor. 
The  following  table  gives  the  comparative  costs  of  the  hol- 
low-tile and  Melan  floors.* 


Material. 

Hollow-tile  Floor 

(see  Fig.  30). 
Total  load  =  150 
lbs.  per  sq.  ft. 

Melan. 

Total  load  =  150  lbs.  per  sq.  ft. 

6'  8"  Span 
(see  Fig.  33). 

20'  Span 
(see  Fig.  34). 

Beams,     connections,  tie-rods, 

Cts. 

j  11.44  1DS-  @ 

|            3  c.  =  34.3 

Cts. 

j  10.12  lbs  @ 
/             3  c.  =  30.4 
1.8  lb.  @  3*  c.  =  6.3 
M 
4 

16    "     @2C.  =  32 

6 
92.7 

Cts. 

j  4.95  lbs.  @ 
i             3  c.  =  14.9 
a.25lbs.@3£c.=  7.9 
20 
7 

13  "     @.  2  C.=  26 

75-8 

26 
2 

l6"@2C  =  32 

94-3 

CHICAGO  BUILDING  LAWS — FLOOR  ARCHES. 

The  following  requirements  are  specified  in  the  Chicago 
building  ordinance,  Section  117  :  "  The  filling  between  the 
individual  iron  or  steel  beams  supporting  the  floors  of 
fire-proof  buildings  shall  be  made  of  brick  arches,  or  con- 
crete arches,  or  hollow-tile  arches,  or  Spanish  tile  arches. 
Brick  arches  shall  not  be  less  than  4  inches  thick,  and  shall 
have  a  rise  of  at  least  1^  inches  to  each  foot  of  span  between 
the  beams.  If  the  span  of  such  arches  is  more  than  5  feet, 
the  thickness  of  the  same  shall  not  be  less  than  8  inches.  If 


*  See  Transactions  Am.  Soc.  Civil  Engin  ers,  vol.  xxxi.  No.  4. 


FLOORS  AND  FLOOR  FRAMING.  75 

hollow-tile  arches  having  a  straight  soffit  are  used,  the 
thickness  of  such  arches  shall  not  be  less  than  at  the  rate  of 
\\  inches  per  each  foot  of  span.  If  Spanish  tile  arches  are 
used,  they  are  to  be  made  as  per  the  published  formulae  of 
the  Guastavino  Construction  Company,  subject  to  the  verifi- 
cation and  approval  of  the  Commissioner  of  Buildings.  If 
concrete  arches  are  used,  the  concrete  in  the  same  shall  not 
be  strained  more  than  100  pounds  per  square  inch,  if  the 
concrete  is  made  of  crushed  stone,  nor  more  than  50  pounds 
per  square  inch,  if  the  concrete  is  made  of  cinders.  In  all 
cases,  no  matter  what  the  material  or  form  of  the  arches 
used,  the  protection  of  the  bottom  flanges  of  the  beams 
and  so  much  of  the  web  of  the  same  as  is  not  covered  by 
the  arches  shall  be  made  as  before  specified  for  the  cover- 
ing of  beams  and  girders." 

Again,  Section  88  :  "  Hollow  tile  and  porous  terra-cotta 
may  be  used  in  the  form  of  flat  arches  for  the  support 
of  floors  and  roofs  ;  such  floor  arches  having  a  height  of  at 
least  \\  inches  for  each  foot  of  span.  The  arches  must  be 
so  constructed  that  the  joints  of  the  same  point  to  a  com- 
mon centre  ;  the  butts  of  the  arches  shall  be  carefully  fitted 
to  the  beams  supporting  them  ;  and  there  shall  be  a  cross- 
rib  for  every  6  inches  or  fractional  part  thereof  in 
height ;  and  in  addition  to  these  there  shall  also  be  diag- 
onal ribs  in  the  butts.  Floor  arches  made  in  the  form  of  a 
segment  of  a  circle  or  ellipsis  must  be  constructed  upon  the 
same  principles,  but  in  such  cases  the  individual  voussoirs 
forming  the  arch  shall  not  be  less  in  height  than  one  thir- 
tieth of  the  span  of  the  arch.  Such  arches,  whether  flat  or 
curved,  shall  have  their  beds  well  filled  with  mortar,  and  the 
centres  shall  not  be  struck  until  the  mortar  has  been  set." 

Before  leaving  the  subject  of  fire-proof  floors  it  will  be 
well  to  mention  the  test  of  hollow-tile  arches  provided  in 
the  case  of  the  Chicago  Athletic  Club  Building,  before 


76 


A  R CHITE C T URA  L  ENGINEERING . 


mentioned.  The  steel  beams  where  not  fire-proofed  were 
badly  bent  where  the  ends  were  not  held,  but  the  metal 
portions  were  in  perfect  condition  where  the  fire-proofing 
remained  intact.  Not  a  single  floor  arch  fell,  and  "  tests 
since  made  on  the  worst-looking  ones  have  developed  a 
sustaining  capacity  of  450  lbs.  per  square  foot  without 
sign  of  rupture." 

The  arches  treated  of  in  this  article,  as  affecting  the 
method  of  design  of  the  floor-beams,  girders,  and  columns, 
are  the  ordinary  tile  arches — be  they  of  the  older  Pioneer 
construction,  the  Lee  form,  or  the  newer  arches  similar  to 
the  Johnson  type. 

FLOOR  LOADS. 

Before  considering  the  most  economical  arrangement 
of  floor-beams,  the  question  of  loads,  which  will  largely 
govern  the  design  of  the  floor  system,  must  be  examined. 
The  loads  in  building  construction  may  be  classified  as 
dead,  live,  wind,  and  eccentric  loads.  These  will  all  be 
considered  in  their  proper  places  in  these  pages.  The  prin- 
cipal loads  affecting  the  floor  system  are  : 

Dead  Loads,  comprising  all  of  the  static  loads  due  to  the 
constructive  parts  of  the  building,  stationary  machinery, 
water-tanks,  and  any  other  permanent  loads. 

Live  Loads,  comprising  the  people  in  the  building,  office 
furniture,  movable  stocks  of  goods,  small  safes  (large  safes 
require  special  provision),  or  varying  loads  of  any  character. 

The  maximum  live  load  per  square  foot  is  usually  as- 
sumed as  follows : 

For  crowd  of  people   80  lbs. 

For  floors  of  houses   40  " 

\    For  theatres  and  churches   80  " 

For  ball-rooms  or  drill-halls   90  " 

For  warehouses,  etc  from  250   "  up. 

For  factories  200  to  450  lbs. 


FLOORS  AND   FLOOR  FRAMLNG.  77 

While  80  lbs.  is  the  maximum  possible  live  load  per 
square  foot  from  a  crowd  of  people  (unless  dancing  be  con- 
sidered), still  we  can  hardly  expect  to  realize  any  such 
load  under  the  conditions  governing  an  office  building. 
Large  crowds  very  seldom  collect  in  offices,  except,  per- 
haps, on  the  two  or  three  lower  floors  devoted  to  stores  or 
banking  purposes,  and  greater  allowances  are  generally 
made  for  such  places.  The  ordinary  office  furniture  will 
certainly  not  exceed,  and  seldom  equal,  the  weight  allowed 
for  persons,  and  hence  additional  security  is  introduced. 
Prof.  Baker,  in  his  "  Treatise  on  Masonry  Construction," 
gives  10  lbs.  per  sq.  ft.  movable  load  for  dwellings,  20  lbs. 
for  large  office  buildings,  100  lbs.  for  churches,  theatres, 
etc.,  and  from  100  to  400  lbs.  for  stores,  warehouses,  and 
factories,  according  to  contents. 

A  20-lb.  unit  load  in  office  buildings,  as  recommended 
by  Prof.  Baker,  might  be  seriously  questioned,  and  late 
experiments  in  this  direction  would  seem  to  sustain  the 
criticism.  While  20  lbs.  per  square  foot  may  be  amply  suf- 
ficient for  average  loads  at  present,  we  must  remember  that 
the  use  of  an  average  is  always  dangerous,  while  provision 
should  be  made,  but  not  recklessly,  for  all  possibilities  of  ex- 
tremes, either  present  or  future.  An  article  in  the  Ameri- 
can Architect,  August  26,  1893,  gives  the  results  of  some 
experiments  made  by  Messrs.  Blackall  &  Everett,  Boston 
architects,  on  the  actual  weights  of  all  moving  loads  in 
some  of  the  larger  Boston  office  buildings.  The  loads  con- 
sidered were  those  due  to  people  and  all  possible  movable 
articles,  including  all  office  fittings  except  such  as  were  a 
part  of  the  floors  or  partitions,  radiators  excepted.  The 
results  were  as  follows:  In  210  offices  in  the  Rogers,  Ames, 
and  Adams  buildings,  an  average  of  16.3  lbs.  per  sq.  ft 
was  found  for  the  Rogers  Building,  17  lbs.  for  the  Ames 


78 


ARCHITECTURAL  ENGINEERING. 


and  16.2  lbs.  for  the  Adams  Building.  The  greatest  moving 
load  in  any  one  office  in  the  three  buildings  was  40.2  lbs.  per 
sq.  ft.,  while  the  average  for  the  heaviest  ten  offices  in  each 
of  these  buildings  was  33.3  lbs.  per  sq.  ft.  Mr.  Blackall 
concludes :  "  If  these  figures  are  to  be  trusted  to  any  extent 
whatever,  then  even  under  the  most  extreme  circum- 
stances, taking  the  pick  of  the  heaviest  offices  in  the  city 
and  combining  them  into  one  tier  of  ten  stories,  the  average 
load  per  square  foot  would  be  only  a  trifle  over  33  lbs.,  while 
for  all  purposes  for  strength,  an  assumption  of  20  lbs.  would 
be  amply  sufficient  in  determining  the  loads  on  the  foun- 
dations, as  well  as  on  the  columns  of  the  lower  stories/' 

With  a  proper  provision,  then,  for  maximum  loads  in 
the  floor  system,  the  20  lbs.  recommended  by  Prof.  Baker 
is  not  enough,  though  safe,  perhaps,  for  an  average.  But,  as 
remarked  before,  the  use  of  averages  is  dangerous,  and  it  be- 
comes a  very  nice  problem  to  balance  present  economy  with 
maximum  present  requirements  or  future  possibilities  ;  for 
the  present  weight  per  square  foot  may  not  safely  be  taken 
as  the  maximum  occurring  during  the  life  of  the  building. 
The  municipal  laws  of  New  York  and  Boston  provide  for 
a  moving  load  of  100  lbs.  per  sq.  ft.,  while  those  of  Chicago 
require  70  lbs.  live  load  per.  sq.  ft.  on  the  floor  system,  with 
proper  reductions  for  the  columns  and  footings.  With  a 
proper  regard  for  economy  100  lbs.  per  sq.  ft.  would  cer- 
tainly seem  too  large  ;  80  lbs.  for  the  lower  and  busier  floors, 
and  40  lbs.  for  the  upper  or  office  floors,  are  certainly  safe, 
and  good  averages,  considered  in  all  lights.  These  loads, 
used  in  all  calculations  affecting  the  metal  framing,  must 
not  be  confounded  with  the  required  loads  for  the  strength 
of  the  individual  tile  arches.  While  the  live  load  per 
square  foot  may  be  reduced  over  large  areas  in  proportion- 
ing the  metal-work,  the  maximum  possible  live  load  must 


FLOORS  AND  FLOOR  FRAMLNG. 


79 


still  be  used  when  any  single  floor  arch  is  considered  by 
itself,  or  subjected  to  tests  to  determine  its  strength.  Some 
further  data  on  live  loads  are  given  later  under  a  discussion 
of  the  building  laws  of  New  York,  Boston,  and  Chicago. 

In  the  Mills  Building,  erected  in  San  Francisco  in  1891, 
the  live  loads  were  as  follows: 


The  practice  in  Chicago  seems  to  be  pretty  well  defined 
in  the  matter  of  decrease  of  live  loads  per  sq.  ft.,  as  they 
are  transferred  from  beams  to  girders,  from  girders  to 
columns,  and  thence  down  the  columns  to  the  footings. 
This  practice  is  founded  on  the  supposition  that  it  is  quite 
possible  that  the  beams  may  sometime  have  to  carry  their 
full  capacity  in  live  loads,  while  the  chances  are  increas- 
ingly less  that  the  girders  or  columns  will  ever  be  required 
to  carry  anywhere  near  their  full  capacity,  if  a  full  load 
had  been  assumed.  The  fully  loaded  area  would  probably 
never  be  large,  and  a  girder  or  column  would  rarely,  if 
ever,  lie  in  the  centre  of  such  an  area.  The  effect  of  a  live 
or  moving  load,  causing  vibration  in  the  parts  of  the  struc- 
ture, is  also  gradually  lessened,  as  the  vibration  is  taken  up 
in  the  transfer  of  the  load  from  member  to  member,  so  that 
by  the  time  it  reaches  the  footings  or  foundations  the  live 
load  is  ignored  entirely.  In  fact,  we  can  hardly  imagine 
the  perceptible  effect  on  the  foundations  of  the  people  in 
an  office  building,  as  compared  with  the  infinitely  greater 
dead  load,  due  to  the  structure  itself. 

In  the  Venetian  Building  in  Chicago  the  beams  were 
calculated  for  the  following  live  loads  : 


Beams.    Girders.    Columns.  Footings. 


First  floor  

Second  floor  to  attic. 

Roof  

Rotunda  


60  50  40 

40  30  20 

20  15  10 

60  50  40 


8o 


ARCHITECTURAL  ENGINEERING. 


Upper  floors  ,   35  lbs. 

Second,  third,  and  fourth  floors   60  " 

First  floor   80  " 

Girders  carry  80  per  cent,  columns  50  per  cent. 

The  dead  loads  to  be  considered  in  the  floor  system  in- 
clude the  arch  itself,  beams,  concrete  filling,  floors  (wood, 
marble,  or  mosaic),  ceilings,  and  partitions. 

The  weights  of  the  iron  or  steel  beams  and  tile  partitions 
are  actually  calculated  for  a  typical  floor  plan,  and  then 
rated  at  so  much  per  sq.  ft.  of  floor  surface.  This  is  abso- 
lutely necessar}^  in  regard  to  partitions  in  office  buildings, 
as  they  are  constantly  being  changed  to  suit  the  conven- 
ience of  tenants.  The  weight  of  the  arch  varies  with  the 
depth  ;  the  depth  is  dependent  on  the  span.  In  the  annex 
of  the  Marshall  Field  Building,  Chicago,  the  following 


weights  were  used : 

Flooring,  f-inch  maple   4  lbs. 

Deadening   9  " 

1 5 -inch  tile  arch   45  " 

Iron   12  " 

Plaster   5  " 

Partitions,  3-inch  mackolite   20  " 

Total  ,   95  lbs.  dead  load. 


We  have,  therefore,  for  live  and  dead  loads  as  follows : 


Beams. 

Girders. 

Columns. 

Footings. 

85 

65 

45 

Dead  

95 

95 

95 

95 

Total  

180 

160 

I40 

95 

Store  floors  :  Live.  .... 

95 

75 

55 

Dead  

95 

95 

95 

95 

Total . . . 

190 

170 

150 

95 

FLOORS  AND  FLOOR  FRAMLNG. 


81 


The  dead  loads  assumed  in  the  Old  Colony  Building, 
Chicago  (1893),  comprised: 


Flooring   4  lbs. 

Deadening   18  " 

Tile  arches. .   35  " 

Iron   10  " 

Plaster   5  " 

Partitions   18  " 

Total   90  lbs. 


The  dead  and  live  loads  used  in  the  calculations  of  the 
floor  systems  and  columns  of  this  building  were,  in  pounds 
per  square  foot : 


Beams. 

Girders. 

Columns. 

Footings. 

70 

50 

40 

Dead  

.  90 

90 

90 

90 

Total  .... 

.  160 

140 

130 

90 

The  floors  for  the  Fort  Dearborn  Building  were  calcu- 

lated in  accordance  with  the  following 

data  : 

Dead  Load 

Live  Load. 

Beams. 

Girders. 

Beams. 

Girders. 

85 

85 

125 

110 

75 

75 

70 

60 

Roof  

40 

40 

40 

40 

140 

140 

200 

180 

50 

50 

200 

180 

Skylight  

40 

40 

50 

50 

70 

60 

The  live  load  on  the  beams  from  the  second  to  thir- 
teenth floor  inclusive  was  taken  at  70  lbs.  per  sq.  ft.,  and 
an  additional  load  of  20  lbs.  per  sq.  ft.  was  added  to  the 
dead  load  to  care  for  all  partitions  which  were  likely  to  be 
moved  at  any  time. 

The  girders  were  figured  for  partition  loads  at  20  lbs. 


82 


ARCHITECTURAL  ENGINEERING. 


per  sq.  ft.  for  all  movable  partitions,  and  for  the  actual 
loads  of  the  main  partitions. 

The  live  load  on  the  columns  was  taken  at  50  lbs.  per 
sq.  ft.  from  the  second  to  the  twelfth  floor  inclusive,  plus 
the  girder  reactions  for  partitions. 

The  following  table  gives  the  unit  loads  used  in  figuring 
the  columns : 


Live  Load 
on 
Floor. 

Live  Load 
on  Columns 
from  Floors 
above. 

1  otai  L,oaa 
on 

Columns. 

40 

13th  floor. . . 

50 

40 

40 

12th    "  ... 

45 

85 

nth    "  ... 

41 

126 

10th    "  ... 

35 

161 

gth    "  ... 

3i 

192 

8th    "  ... 

25 

217 

7th    «  ... 

21 

238 

6th    "  ... 

15 

253 

5th    "  ... 

11 

264 

4th    "  ... 

5 

269 

3d     "  ... 

1 

270 

2d     "  ... 

0 

270 

1st    "  ... 

125 

0 

270 

Basement. . 

50 

320 

The  dead  load  on  the  floor-beams  was  made  up  as  fol- 
lows, a  9"  porous  end-construction  arch  having  been  used : 

9"  arch   26  lbs.  per  sq.  ft. 

9"  21-lb.  I  beams   4  "  " 

6  to  1  cinder  concrete   30   "  " 

Mosaic  and  wood  floors,  average..  10  "  " 

Plaster...    6  "  " 


Total 


76 


FLOOR  FRAMING— BEAMS. 

The  distance  centre  to  centre  of  the  floor-beams  must 
be  determined  with  reference  to  the  type  of  floor  arch 
used.  Ordinary  practice  in  Chicago  skeleton  construction 
has  made  from  5  to  6  feet  the  usual  span  for  tile  arches,  in 


FLOORS  AND  FLOOR  FRAMING. 


83 


panels  01  ordinary  lengths;  but  in  cases  where  the  columns 
are  spaced  a  considerable  distance  apart  the  floor-beams  are 
placed  nearer  together.  Reference  to  Figs.  18  and  19  will 
show  the  practice  in  beam-spacing  in  late  examples  of 
skeleton  buildings  in  Chicago. 

The  most  economical  arrangement  of  floor-beams  has 
had  little  investigation,  and  there  seems  to  be  no  uni- 
formity of  practice.  If  the  framing  plans  could  be  so 
arranged  that  the  floor-beams  and  girders  would  be  strained 
to  the  full  allowable  fibre  strain,  it  would  certainly  be  more 
economical  than  where  the  framing  plans  require  the  use  of 
beams  heavier  than  those  actually  needed.  Take,  for  ex- 
ample, a  framing  plan  calling  for  a  bending  moment  in  a 
floor-beam  of  65,000  foot-pounds.  This  would  require  a 
moment  of  resistance  of  48.72.  The  moment  of  resistance 
for  a  12"  40-lb.  beam  is  only  46.9,  while  R  for  a  15"  41-lb. 
beam  is  56.6.  The  latter  would  have  to  be  used,  with  an 
excess  in  strength  of  some  16  per  cent;  and  if  such  panels 
occurred  frequently  in  a  floor  system,  an  excess  of  16  per 
cent  would  therefore  occur  throughout.  Hence  an  eco- 
nomical framing  plan  would  be  one  in  which  the  beams 
are  so  arranged  in  span  and  distance  centre  to  centre,  as 
to  carry  a  given  floor  load  with  the  beams  strained  to  the 
full  allowable  fibre  strain.  A  very  small  variation  may 
make  this  possible  or  impossible. 

Again,  it  is  seldom  economical  to  use  the  heaviest 
weight  of  any  depth  of  beam,  if  a  deeper  beam  can  be  used. 
There  is  necessarily  a  great  waste  of  material  toward  the 
ends  of  heavy  rolled  beams,  and  as  the  strength  increases 
as  the  square  of  the  depth,  the  deeper  beam  is  always  the 
more  economical.  Thus  the  moment  of  resistance  for  a  12" 
32-lb.  beam  is  37,  while  the  \o"  33-lb.  beam  has  R  —  32.3. 
The  former  is  lighter,  and  far  stronger.  A  20"  64-lb.  beam 
is  also  stronger  than  a  15"  80-lb.  beam. 


84 


A  R  CHITE  CTURA  L  ENGINEERING. 


The  coefficient  for  a  15"  50-lb.  beam  is  753,000. 

"  "  15"  55-lb.  "  «  792,000. 
"   "  15"  60-lb.     "     "  916,300. 

Hence  the  use  of  a  15"  55-lb.  beam  is  not  economical,  as  the 
coefficient  does  not  vary  between  the  50-  and  60-lb.  limits 
in  proportion  to  the  weight.  For  a  uniformly  distributed 
load  these  coefficients  are  obtained  by  multiplying  the 
load,  in  pounds  uniformly  distributed,  by  the  span  length 
in  feet.  If  the  load  be  concentrated  at  the  centre  of  the 
span,  multiply  the  load  by  2,  and  then  consider  it  as  uni- 
formly distributed.  The  maximum  coefficients  of  strength 
for  I  beams  of  different  depths  and  weights  are  usually 
given  in  the  pocket  companions  issued  by  the  various  steel 
companies.  The  handbook  of  Carnegie,  Phipps  &  Co.  is 
generally  used  by  architects  and  engineers.  In  that  book 
the  maximum  permissible  coefficients  are  given  for  all  of 
the  ordinary  rolled  shapes,  on  a  basis  of  16,000  lbs.  per 
square  inch  fibre  strain,  and  also  on  a  basis  of  12,500  lbs. 
per  square  inch  fibre  strain.  The  former  is  generally  used 
in  building  work. 

The  distribution  of  the  material  in  the  cross-section 
affects  the  moment  of  inertia,  and  hence  R.  The  sections 
from  some  mills  will  be  found  better  than  those  from 
others  in  this  respect. 

Care  must  be  taken  in  figuring  floor-beams  to  see  that 
the  length  of  clear  span  is  not  too  great,  giving  a  deflection 
sufficient  to  crack  the  plaster  ceiling  beneath.  A  deflec- 
tion of  about  3^-5-  of  the  clear  span,  or  ^  of  an  inch  per 
foot,  has  been  found  by  experiment  and  practice  to  be  the 
maximum  permissible  deflection — or  d  =  L  X  0.33,  where 
d  =  greatest  allowable  deflection  in  inches,  at  centre  of 
beam,  and  L  —  length  of  span  in  feet.  This  safe  deflection 
limit  is  also  indicated  for  each  size  and  weight  of  beam 


/ 


FLOORS  AND  FLOOR  FRAMING. 


85 


given  in  the  tables  for  uniformly  loaded  I  beams  in  the 
handbook  of  Carnegie,  Phipps  &  Co. 

Lateral  stiffness  may  also  need  consideration  in  some 
cases.  Where  the  floor-beams  are  of  the  same  depth  as  the 
girders,  "  coping  "  is  necessary,  or  a  cutting  away  of  the 
ends  of  the  floor-beams  to  fit  against  the  flanges  of  the 
girders.  About  \  inch  clearance  is  usually  allowed  be- 
tween floor-beams  and  girders,  and  \  inch  between  columns 
and  girders.    This  is  sufficient  for  easy  erection. 

The  standard  connection-angles  manufactured  by  Car- 
negie, Phipps  &  Co.  are  generally  used  whenever  prac- 
ticable, as  connections  between  floor-beams  and  girders. 
These  connection-angles  are  given  for  the  various  depths 
and  weights  of  steel  and  iron  beams  in  the  handbook. 
They  are  designed  on  a  basis  of  10,000  lbs.  allowable 
shearing-strain,  and  20,000  lbs.  bearing  on  rivets  or  bolts 
per  square  inch,  and  are  usually  of  sufficient  strength  for 
regular  details  as  found  in  practice.    The  adoption  of  such 

n  7», 


611  /-ii  /  »,  ~ii_m 
x6x]6L.O-|OLPiN6:„ 


H°LE5 

^  rivet; 


m 


± 


-S3 


K8F  fm 

CONNECTION  L 
I53TEELP-4J-5^80LB}. 

Fig.  41. 


uniform  "  standards  "  is  certainly  a  great  help  to  the  mills 
and  bridge  or  iron  shops,  as  well  as  to  the  designer,  but  in 
the  hands  of  the  careless  or  ignorant  designer  is  apt  to 
be  an  element  of  weakness.  From  careful  observation  of 
building  methods  as  practiced  in  Chicago,  the  writer  is 
convinced  that  faulty  details  constitute  an  even  greater 
part  of  the  defects  in  the  general  run  of  buildings,  than 


86 


ARCHITECTURAL  ENGINEERING. 


arises  from  poor  materials  employed,  or  imperfect  general 
features  of  design.  Any  "  standards  "  are  therefore  to  be 
used  with  caution,  as  they  tempt  the  careless  designer  to 
use  them  under  all  conditions,  whether  they  be  adequate  or 
not.    They  are  standard,  hence  they  must  be  all-sufficient. 

x6xj|  L-o-5l°ng 


H°L&5 
_pOR 


*RIVET3|?M  m\ 

CONNECTION  L. 
poR  8"^ND9"5TCCLl5EaM5. 

Fig.  42. 

Figs.  41  and  42  show  standard  connection-angles  for  the 
beams  as  given. 

GIRDERS. 

The  girders,  running  from  column  to  column,  support  the 
floor-beams,  and  transfer  their  loads  directly  to  the  columns. 
As  before  mentioned,  it  is  often  necessary  to  use  two  I  beams 
side  by  side  as  a  girder,  or  even  plate  or  latticed  girders 
in  longer  spans  or  under  special  loads.  Separators  should 
always  be  used  in  the  case  of  double  beams,  in  order  to 
equalize  the  loads  on  the  two  beams,  and  also  to  act  as 
spacers,  keeping  them  a  proper  distance  apart.  Carnegie's 
separators  are  generally  taken  as  standard. 

It  is  quite  impracticable  to  make  any  comparisons  as  to 
the  relative  economy  of  short  spans  for  girders  with  many 
columns,  and  fewer  columns  with  longer  girders.  Both 
types  are  to  be  found  in  Chicago,  even  to  extremes,  but 
they  are  usually  the  results  of  conditions,  rather  than  at- 
tempts at  economy.  The  conditions  governing  the  design 
of  any  particular  building  are  usually  so  potent  that  the  rule 
in  one  case  might  prove  the  exception  in  the  next.  The 
arrangement  of  the  exterior  piers,  the  architectural  effect 
striven  for,  the  arrangement  and  proper  planning  of  the 


FLOORS  AND  FLOOR  FR A  Ml JVC  8/ 

interior  for  the  uses  intended,  all  govern,  in  a  great  meas- 
ure, the  placing  of  the  supporting  columns,  and  hence  the 
girder  lengths.  Thus  in  Fig.  18,  showing  the  framing  plan 
of  the  new  Fort  Dearborn  Building,  two  9-inch  beams  or  two 
10-inch  beams  are  generally  used  as  girders,  while  in  Fig.  19, 
of  the  Reliance  Building,  single  beams  are  used  as  girders 
in  all  cases.  In  the  Woman's  Temple,  Chicago,  Burnham 
&  Root,  architects,  the  floor-beams  are  nearly  all  30  feet 
long,  and  the  girders  likewise,  15-in.  I  beams  having  been 
used  throughout ;  while  in  the  new  Marshall  Field  Build- 
ing, by  the  same  architects,  a  20-foot  panel  was  used. 

In  office  buildings  the  panels  are  often  made  of  such 
dimensions  as  to  give  two  suitable  office  widths  from  centre 
to  centre  of  piers.  Thus  the  practice  of  Holabird  &  Roche, 
architects,  is  to  space  the  exterior  and  interior  columns  23 
feet  centres  where  possible,  making  two  offices  of  11  ft. 
6  in.  in  each  bay  (see  Fig.  16). 

A  point  to  be  remembered  in  the  design  of  girders  is 
that  a  much  more  economical  girder  can  be  had  when  two 
floor-beams  are  to  be  supported  than  three  ;  or  an  even 
number  instead  of  an  odd  number  of  beams.  In  the  latter 
instance  a  load  will  occur  at  or 
near  the  centre  of  the  girder,  re- 
sulting in  a  much  greater  bend- 
ing moment.  If  but  two  beams 
are  used,  the  arm  is  but  one  third 
the  span  of  the  girder.  All  of  the 
floor-beams  and  girders  in  the 
floor  system  are  usually  so  ar- 
ranged as  to  be  flush  on  the  under 
sides,  as  shown  in  Fig.  43.  This  is  to  provide  for  the 
plastered  ceiling.  The  inequalities  in  the  arch  depths  are 
made  up  in  the  concrete  filling. 


Fig.  43. 


CHAPTER  V. 

EXTERIOR  WALLS— PIERS. 

The  subject  of  the  exterior  piers  which  carry  their 
tributary  floor  and  roof  loads,  besides  the  weight  of  the 
walls  themselves,  is  capable  of  three  separate  treatments, 
each  of  which  is  used  under  its  own  peculiar  circumstances. 

First.  Where  the  outside  piers  are  constructed  entirely 
of  masonry,  carrying  all  of  the  wall-,  floor-v  and  roof-loads 
which  come  on  them,  by  means  of  masonry  alone.  Such 
construction  is  used  in  buildings  of  moderate  height,  and 
constitutes  the  ordinary  type  of  building.  But  in  the 
higher  structures  of  from  sixteen  to  twenty  stories,  which 
are  here  being  considered  in  particular,  it  is  the  rare  excep- 
tion, at  the  present  time,  to  rely  entirely  on  masonry  piers. 

The  objections  to  such  piers  of  solid  masonry  are  three- 
fold : 

a.  The  modern  requirements  of  plenty  of  light  and  air 
in  all  offices,  demand  that  the  windows  be  broad  and 
numerous  and  the  piers  narrow.  In  the  highest  buildings 
of  the  present  day  hardly  any  masonry  construction  is 
strong  enough  to  carry  the  necessary  roof-  and  floor-loads 
besides  its  own  weight,  for  so  great  a  height  and  with  so 
small  a  cross-section  as  is  desired.  There  are  prominent 
office  buildings  in  Chicago  and  elsewhere,  in  which  the  ex- 
terior walls  carry  their  proper  share  of  all  loads ;  but  a 
little  observation  will  show  that  in  high  buildings  of  this 
type  the  comforts  of  the  tenants  have,  in  a  large  measure, 
been  sacrificed  for  architectural  effect. 

b.  The  second  objection  to  such  large  masonry  piers  is 

88 


EXTERIOR   WALLS— PIERS.  89 

that  they  take  up  too  much  valuable  renting-space.  When 
the  rent  of  offices  is  proportioned  at  so  much  per  square 
foot,  this  becomes  a  matter  of  no  inconsiderable  importance 
to  the  owner. 

c.  The  weight  of  these  solid  masonry  piers  would  so  add 
to  the  load  per  square  foot  on  the  clay  or  foundations  that 
many  of  the  most  remarkable  examples  of  architectural 
engineering  would  be  well-nigh  impossible. 

In  the  new  Marshall  Field  Building  in  Chicago,  masonry 
piers  were  used  to  carry  all  exterior  loads,  but  a  mercan- 
tile structure  does  not  present  as  exacting  conditions  as 
an  office  building,  and  the  exterior  piers  may  be  widened 
for  architectural  effect  without  seriously  inconveniencing 
the  plan  of  the  interior. 

Second.  The  second  treatment  of  which  the  exterior 
piers  are  capable  is  that  in  which  metal  columns,  carrying 
the  tributary  floor  and  roof  loads,  are  placed  inside  the 
masonry  piers,  while  the  latter  support  themselves  and  the 
"  spandrels"  only.  The  spandrels  constitute  those  portions 
of  the  exterior  walls  lying  between  the  piers  and  over  and 
under  the  window-spaces. 

If  this  method  is  employed,  great  care  must  be  taken 
that  the  masonry  does  not  touch  the  columns,  in  order  that 
the  unequal  settlement  of  the  metal- work  and  the  masonry 
may  not  cause  undesirable  strains.  On  account  of  the 
numerous  mortar-joints,  the  masonry  will  settle  much 
faster  than  will  the  metal  columns  under  the  gradual  settle- 
ment of  the  whole  structure.  As  an  example  of  initial  com- 
pression in  freshly  laid  mortar,  Mr.  Geo.  B.  Post,  archi- 
tect of  the  New  York  Produce  Exchange  building,  states 
that  a  measured  height  of  9'  6"  at  the  time  of  building, 
compressed  about  \"  under  a  maximum  pressure  of  62  lbs. 
per  square  inch  of  base,  induced  by  the  finished  wall.  The 
whole  wall  was  built  very  rapidly. 


90 


ARCHITECTURAL  ENGINEERING. 


If,  then,  the  masonry  bears  on  rivet-heads,  plates,  or 
connections  on  the  columns,  a  heavy  strain  is  produced 
which  has  not  been  provided  for.  Great  care  is  necessary 
in  such  combinations  of  metal  columns  and  masonry  piers 
to  leave  sufficient  "  open  joints  "  at  points  over  cornices 
and  the  like,  where  they  will  least  be  noticed,  to  allow  for 
such  settlement.  Also  where  the  mass  is  not  homogeneous, 
as  in  stone  facing  and  brick  backing,  the  result  is  likely  to 
be  that  the  stone,  with  fewer  mortar-joints,  settles  less  and 
receives  more  than  its  share  of  the  load,  thus  producing 
cracks  and  spalling  off  the  angles.  This  was  the  case  in  the 
old  portion  of  the  Washington  Monument. 

The  objections  of  size  and  weight  will  also  hold  in  the 
piers  of  this  type,  as  in  the  first  method,  if  the  building  be 
very  high.  Thus  in  the  Masonic  Temple  of  twenty  one 
stories,  metal  columns  of  plates  and  angles  were  placed 
within  the  masonry  piers,  but  it  was  found  that  the  maxi- 
mum allowable  pressure  of  12  tons  per  square  foot  on  brick- 
work, as  used  by  the  engineer,  would  be  reached  at  the 
level  of  the  fifth  floor ;  hence  below  that  level  the  load  ex- 
ceeded the  safe  compressive  resistance  of  the  material ;  and 
this  without  any  floor  or  roof  loads,  as  the  latter  were 
carried  by  the  metal  columns  within  the  piers.  The  ex- 
pedient was  therefore  adopted  of  carrying  the  masonry- 
work  on  brackets  attached  to  the  metal  columns  at  the 
sixteenth-  and  fifth-story  levels,  thus  making  the  pier  con- 
sist of  three  separate  columns  of  masonry,  and  the  one 
continuous  metal  column. 

Third.  The  third  method  of  constructing  the  exterior 
piers  is  the  one  more  approved  at  the  present  stage  of 
architectural  engineering — the  one  which  has  undoubtedly 
opened  up  the  means  for  building  the  highest  structures. 
In  this,  all  weights  are  thrown  on  the  metal  columns,  which, 
in  place  of  solid  piers,  are  surrounded  with  a  protective 


EXTERIOR   WALLS— PIERS.  9 1 

shell  or  covering  only,  made  of  ornamental  terra-cotta  or 
brickwork,  securely  anchored  to  and  supported  by  the 
columns  at  the  various  floor  levels. 

This  construction  undoubtedly  gives  the  minimum 
weight  per  foot  of  height,  and  makes  possible  such  small 
piers  as  are  indispensable  for  light  and  desirable  offices. 
The  "  Chicago  type  "  is  a  popular  name  for  this  method  ; 
a  type  which  has  developed  fast  and  remarkably  during  the 
past  ten  years  of  Western  architecture,  while  the  height  of 
municipal  buildings  has  been  increasing  steadily  from  ten 
to  twenty  stories.  The  increasing  value  of  ground-space, 
the  demands  for  rapid  construction,  and  the  necessity  for 
the  lightest  possible  loads  on  the  subsoil,  have  all  con- 
tributed to  the  success  of  this  type. 

Chicago  construction  thus  does  away  with  masonry  as 
a  supporting  member,  and  the  load-bearing  brick  wall  or 
masonry  pier  is  replaced  by  an  envelope  of  terra-cotta  or 
brickwoik,  enclosing  the  steel  columns  and  filling  the  span- 
drels or  spaces  between  the  windows.  This  envelope  is 
not  used  as  a  strengthener  to  the  supporting  members,  but 
as  a  protection  against  the  elements  and  the  dangers  of 
fire.  The  brick  wall,  once  the  fundamental  factor  in  build- 
ing construction,  now  fulfils  simply  a  decorative  and  pro- 
tective function.  The  great  possibility  for  external  effect 
through  this  use  of  brick  and  terra-cotta  in  connection  with 
skeleton  construction,  has  opened  up  a  vast  market  to  the 
manufacturers  of  fine  qualities  of  face-brick,  moulded  brick, 
and  terra-cotta  in  all  its  varieties. 

The  terra-cotta  companies  design  their  pieces  with 
special  reference  to  tying  them  to,  or  suspending  them 
from  such  a  framework;  so  that,  in  reality,  the  building 
becomes  nothing  more  nor  less  than  a  vital  skeleton  of  steel, 
with  an  architectural  and  protective  wrapper  of  terra-cotta, 
tile,  or  brickwork,  inside  and  outside.    The  terra-cotta 


92 


ARCHITECTURAL  ENGINEERING. 


arches,  which  to  the  casual  observer  seem  to  carry  some 
heavy  wall  or  pier  above,  prove  to  be  made  of  hollow  clay 
blocks,  held  by  wires  or  clamps  to  the  concealed  beams  or 
girders  which  really  support  the  loads. 

Brick  and  terra-cotta  are  generally  preferred  to  other 
building  materials  for  the  exterior  walls  of  a  tall  building, 
on  account  of  the  ease  with  which  they  may  be  handled 
as  well  as  for  the  facility  with  which  they  may  be  built 
into  and  about  the  forms  of  beams  and  columns.  Stone 
has  gradually  been  driven  from  the  field  of  skeleton  con- 
struction in  exterior  walls,  except  as  used  in  the  lower 
stories  only,  as  a  base  for  the  superimposed  brick  or  terra- 
cotta work.  This  has  been  due  to  the  difficulty  experi- 
enced in  properly  attaching  the  masses  of  stone  to  the 
metal  framework.  Stone  has  also  been  used  in  thin  slabs 
in  the  lower  stories,  as  in  the  first  floor  of  the  Reliance 
Building,  where  highly  polished  slabs  of  granite  were  en- 
closed in  ornamental  frames  or  grilles  of  metal-work  sur- 
rounding the  columns,  as  shown  in  lower,  part  of  Fig.  44. 
Fig.  45  shows  the  girder  over  the  main  entrance  to  the 
Masonic  Temple. 

In  order  to  render  the  exterior  impervious  to  moisture, 
and  thus  protect  the  metal  framing  against  corrosion,  only 
the  very  hardest  and  most  thoroughly  burned  brick  should 
be  used.  Portland  cement  mortar  is  also  specified  in  the 
best  classes  of  work,  with  well-filled  joints  and  careful 
bonding  and  anchoring.  In  other  words,  less  is  now  re- 
quired of  the  brick  wall  as  a  supporting  member  than 
formerly,  when  the  walls  fulfilled  the  function  of  bearing 
dead  loads  only ;  but  much  more  is  now  demanded  of  it  as 
to  quality  and  perfection  of  workmanship,  and  hence  a 
better  constructed  and  more  thoroughly  knit  wall  has  re- 
sulted in  the  best  examples  of  Chicago  construction. 

The  Chicago  building  ordinance  defines  skeleton  con- 


94 


ARCHITECTURAL  ENGINEERING. 


struction  as  follows  :  "  The  term  '  skeleton  construction ' 
shall  apply  to  all  buildings  wherein  all  external  and  internal 
loads  and  strains  are  transmitted  from  the  top  of  the  build- 
ing to  the  foundations  by  a  skeleton  or  framework  of  metal. 
In  such  framework  the  beams  and  girders  shall  be  riveted 


Fig.  45. — Section  over  Main  Entrance,  Masonic  Temple. 

to  each  other  at  their  respective  junction  points.  If  pillars 
made  of  rolled  iron  or  steel  are  used,  their  different  parts 
shall  be  riveted  to  each  other,  and  the  beams  and  girders 
resting  upon  them  shall  have  riveted  connections  to  unite 


EXTERIOR   WALLS— PIERS.  95 

them  with  the  pillars.  ...  If  buildings  are  made  fire-proof 
entirely,  and  have  skeleton  construction  so  designed  that 
their  enclosing  walls  do  not  carry  the  weight  of  floors  or 
roof,  then  their  walls  may  be  reduced  in  thickness  one 
third  from  the  thickness  hereinafter  provided  for  walls  of 
buildings  of  the  different  classes,  excepting  only  that  no 
wall  shall  be  less  than  12  inches  in  thickness;  and  pro- 
vided, also,  that  such  walls  shall  be  thoroughly  anchored 
to  the  iron  skeleton ;  and  provided,  also,  that  wherever  the 
weight  of  such  walls  rests  upon  beams  or  pillars,  such 
beams  or  pillars  must  be  made  strong  enough  in  each  story 
to  carry  the  weight  of  wall  resting  upon  them  without  reli- 
ance upon  the  walls  below  them.  But  if  walls  of  hollow 
tiles  are  used  as  filling  between  the  members  of  the  skeleton 
construction,  they  shall  be  of  the  full  thickness  specified  for 
non-skeleton  buildings." 

The  requirements  for  protecting  external  structural 
members  of  iron  and  steel  are  defined  as  follows  :  "  All  iron 
or  steel  used  as  a  supporting  member  of  the  external  con- 
struction of  any  building  exceeding  90  feet  in  height  shall  be 
protected  as  against  the  effects  of  external  changes  of  tem- 
perature and  of  fire  by  a  covering  of  brick,  terra-cotta,  or 
fire-clay  tile,  completely  enveloping  said  structural  members 
of  iron  and  steel.  If  of  brick,  it  shall  be  not  less  than  8 
inches  thick.  If  of  hollow  tile,  it  shall  be  not  less  than  6 
inches  thick,  and  there  shall  be  at  least  two  sets  of  air- 
spaces between  the  iron  and  steel  members  and  the  outside 
of  the  hollow-tile  covering.  In  all  cases  the  brick  or 
hollow  tile  shall  be  bedded  in  mortar  close  up  to  the  iron 
or  steel  members,  and  all  joints  shall  be  made  full  and  solid. 

"  Where  skeleton  construction  is  used  for  the  whole  or 
part  of  a  building,  these  enveloping  materials  shall  be  inde- 
pendently supported  on  the  skeleton  frame  for  each  indi- 
vidual story. 


96 


ARCHITECTURAL  ENGINEERING. 


"  If  terra-cotta  is  used  as  part  of  such  fire-proof  en- 
closure, it  shall  be  backed  up  with  brick  or  hollow  tile ; 
whichever  is  used  being,  however,  of  such  dimensions  and 
laid  up  in  such  manner  that  the  backing  will  be  built  into 
the  cavities  of  the  terra-cotta  in  such  manner  as  to  secure 
perfect  bond  between  the  terra-cotta  facing  and  its  back- 
ing. 

"  If  hollow  tile  alone  is  used  for  such  enclosure,  the 
thickness  of  the  same  shall  be  made  in  at  least  two  courses, 
breaking  joints  with  and  bonded  into  each  other." 

The  New  York  law  prescribes  the  following:  "  Where 
columns  are  used  to  support  iron  or  steel  girders  carrying 
curtain-walls,  the  said  columns  shall  be  of  cast  iron,  wrought 
iron,  or  rolled  steel,  and  on  their  exposed  outer  and  inner 
surfaces  be  constructed  to  resist  fire  by  having  a  casing  of 
brickwork  not  less  than  4  inches  in  thickness  and  bonded 
into  the  brickwork  of  the  curtain-walls,  or  the  inside  sur- 
faces of  the  said  columns  may  be  covered  with  an  outer 
shell  of  iron  having  an  air-space  between  ;  and  the  exposed 
sides  of  the  iron  or  steel  girders  shall  also  be  similarly  cov- 
ered in  and  tied  and  bonded." 

The  first  example  of  a  purely  skeleton  construction  in 
Chicago  occurred  in  the  rear  wall  of  the  Phenix  Building, 
now  the  Western  Union  Telegraph  Building,  by  Burnham 
&  Root,  architects.  In  the  wall  behind  the  elevators, 
cast  columns  were  used  with  two  sets  of  horizontal  supports 
at  each  story.  The  outside  supports  were  made  of  I  beams 
resting  on  brackets  connected  to  the  columns,  these  I  beams 
carrying  a  4|-inch  wall  of  enamelled  brick.  The  inner  sup- 
ports consisted  of  I  beams  placed  between  the  columns, 
supporting  a  4-inch  wall  of  hollow  tile.  Thus  the  wall 
was  formed  of  two  layers  or  "  skins  "  held  together  by  the 
window-frames,  etc.  To  Mr.  W.  L.  B.  Jenney  belongs  the 
credit  of  having  designed  the  first  skeleton  building  erected 


EXTERIOR   WALLS— PIERS. 


97 


in  Chicago;  the  Home  Insurance  Building,  built  in  1883. 
This  structure  also  contained  the  first  Bessemer  steel  beams 
used  in  building  construction. 

To  avoid  any  injury  to  the  walls  or  piers  in  skeleton 
construction  through  the  expansion  and  contraction  of  the 
tall  columns  of  steel,  the  masonry  or  envelope  must  be  so 
constructed  as  to  be  independent  for  each  story  length. 
This  is  provided  by  means  of  shelf-angles  or  brackets  at 
each  and  every  floor  level,  thus  allowing  the  entire  front 
of  the  building  to  be  built  in  such  a  manner  that  any  or 
all  of  the  envelope  or  masonry  facing  may  be  removed  with- 
out injury  to  the  load-bearing  members.  In  the  Home 
Insurance  Building  just  mentioned,  cast  lintels  were  used 
to  form  the  soffits  of  the  windows  at  each  floor,  and  de- 
signed to  carry  the  walls  for  the  story  above. 

Fig.  46  shows  a  corner  pier  from  the  Reliance  Building, 


Fig.  46. — Detail  of  Corner  Pier,  Reliance  Building. 


and  Fig.  47  is  a  plan  of  the  supporting  framework  for 
same. 

A  striking  example  of  what  has  been  made  possible  in 
the  construction  of  exterior  piers  by  skeleton  methods  is 


9» 


ARCHITECTURAL  ENGINEERING. 


shown  in  the  difference  between  the  old  and  new  portions 
of  the  mammoth  Monadnock  Building  in  Chicago  (see 
frontispiece).  At  the  time  of  designing  the  older  portion 
of  this  building,  the  owner,  in  spite  of  the  protests  of  the 
architects,  insisted  on  having  the  conservative  practice  of 
solid  masonry  piers,  which,  for  a  height  of  sixteen  stories, 
resulted  in  walls  some  6  feet  thick  at  the  street  level.  A 
few  years  later  an  addition  was  designed  for  the  south  half 
of  the  block,  seventeen  stories  in  height,  and  the  walls  of 
this  new  building  were  built  in  the  veneer  pattern,  which 


 4i6>.  


' PMT£ -/MB  24'x?s  ' 


SI 


6x6x^6  L. 


Fig.  47. 


had  previously  been  rejected  by  the  owner  of  the  other 
portion.  It  doubtless  proved  an  expensive  lesson  for  the 
first  investor. 

A  brick  wall  carried  to  the  height  of  the  Manhattan 
Life  Insurance  Building  in  New  York  City  (241')  would, 
according  to  the  building  laws  of  most  cities,  have  to  be 
about  6  feet  thick.  Through  the  use  of  skeleton  construc- 
tion the  enclosing  walls  in  this  building  were  made  only  12 
and  16  inches  thick. 

Fig.  48  shows  the  required  thickness  of  walls  under  the 
Chicago  ordinance  for  buildings  devoted  to  the  sale, 
storage,  and  manufacture  of  merchandise.    Fig.  49,  is  for 


EXTERIOR   WALLS— PIERS. 


99 


the  walls  of  hotels,  apartments,  and  office  buildings  of 
construction  other  than  the  skeleton  type.    Fig.  50  shows 


Fig.  48. 


Fig.  49. 


Fig.  50. 


the  requirements  for  masonry  walls  (in  office  buildings) 
which  carry  their  own  weight  only. 


CHAPTER  VI. 


SPANDRELS  AND  SPANDREL  SECTIONS— BAY  WINDOWS, 

The  spandrels  constitute  those  portions  of  the  exterior 
walls,  either  on  the  street  fronts  or  in  the  interior  court, 
which  lie  between  the  piers  and  between  the  window-spaces 
of  successive  stories.  "  Spandrel  sections,"  as  they  are 
called,  must  be  made  for  every  different  type  of  spandrel 
support  in  the  building,  and  they  must  clearly  show  the 
supporting  beams  or  metal-work  required  to  carry  the 
veneer  walls  in  the  manner  desired.  These  sections  vary 
greatly,  depending  largely  on  the  architectural  effect  con- 
templated by  the  designer  in  his  arrangement  of  the  ma- 
terial, and  general  descriptions  of  spandrels  can  hardly  be 
given  as  applicable  to  general  practice.  Illustrations  of 
numerous  examples  will  better  serve  to  show  the  methods 
employed. 

The  spandrel-beams  are  supported  by  the  masonry  piers 
where  such  load-bearing  piers  are  used,  or,  in  the  veneer 
construction,  by  the  metal  columns  in  the  walls.  The  face 
of  the  spandrel-walls  may  be  "  flush  "  with  the  piers,  or 
"  in  reveal,"  that  is,  set  back  from  the  face  of  the  piers.  In 
the  first  case  the  wall  presents  a  nearly  unbroken  surface, 
except  for  the  terra-cotta  sills  and  window-caps,  while  the 
second  method  accentuates  the  piers,  and  throws  the 
spandrel-walls  in  reveal.  The  architectural  treatment  will 
determine  these  conditions.  The  former  case  is  generally  of 
far  simpler  construction,  as  the  spandrel-beams  come  at 
or  near  the  centres  of  the  columns,  thus  avoiding  many  em- 
barrassments in  the  irregular  bracketing  from  the  columns, 

IOO 


SPANDRELS  AND  SPANDREL  SECTIONS. 


IOI 


which  becomes  necessary  in  the  support  of  the  spandrel- 
beams  where  the  spandrel-  or  curtain-walls  are  recessed. 
Fig.  51  shows  a  very  simple  form  of  spandrel  section 


4- 


Fig.  51. 


Fig.  52. 


from  the  Ashland  Block,  Chicago,  where  flush  walls  were 
used.    The  veneer  wall  is  but  9  inches  thick. 

The  use  of  plate  girders,  as  the  main  spandrel  supports, 
is  shown  in  Fig.  52,  which  is  a  section 
taken  from  near  the  corner  of  the  Re- 
liance Building.  The  connections  of 
these  plate  girders  to  the  Gray  columns 
used,  are  shown  in  Fig.  104,  Chapter  VII. 
The  connections  of  the  cast  uprights 
to  support  the  terra-cotta  mullions  be- 
tween the  windows,  are  shown  in  Fig. 
53.  Figs.  54  and  55  are  taken  from 
the  eleventh-  and  twelfth-floor  levels  re- 
spectively of  the  Fort  Dearborn  Build- 
ing.   The  section  given  in  Fig.  56  is  taken  at  the  first-floor 


102 


ARCHITECTURAL  ENGINEERING. 


or  sidewalk  level,  and  shows  the  prismatic  lights  in  the 
sidewalk,  as  well  as  the  small  windows  which  help  to  light 
the  basement  restaurant  space.  Fig.  57  is  a  section  taken 
at  the  attic  floor,  showing  the  main  cornice  and  roof  con- 
struction. 


The  materials  generally  used  for  veneer  buildings  con- 
sist, as  before  stated,  of  pressed  brick  and  terra-cotta,  thr 
latter  being  used  for  the  window-caps  and  sills,  horizontal 
bands,  ornamental  capitals,  brackets,  etc.,  or  even  in  entire 
fronts,  as  seen  in  the  Stock  Exchange  Building,  or  in  the 
Reliance  Building  of  enamelled  terra-cotta. 

The  brick  or  tile  work  of  the  piers  is  usually  supported 
by  bracket-angles,  attached  to  the  columns,  as  has  been 
described  in  Chapter  V,  while  the  body  or  backing  of  the 


1 


Fig.  54- 


Fig.  56. 


104  ARCHITECTURAL  ENGINEERING. 

spandrel-walls  is  supported  directly  by  the  main  spandrel- 
beams,  as  indicated  in  the  previous  figures. 

The  ornamental  terra-cotta  work,  however,  can  seldom 
be  supported  directly  by  the  spandrel-beams,  and  a  system 
of  anchors  must  be  resorted  to,  to  properly  tie  the  individual 


Fig.  57. 


blocks  either  to  the  brick  backing  or  to  the  metal-work 
itself.  These  anchors  are  usually  made  of  \  inch  square  or 
round  iron  rods,  which  are  hooked  into  the  ribs  provided 
in  the  terra-cotta  blocks,  and  then  drawn  tight  to  the  brick- 
work or  metal-work  by  means  of  nuts  and  screw-ends. 


SPANDRELS  AND  SPANDREL  SECTIONS.  105 

Such  anchors  are  shown  in  Fig.  59.  Hook-bolts  are  also 
largely  used,  as  in  Fig.  55,  where  the  ends  are  shown  bent 
around  the  spandrel-channels  or  I  beams.  Clamps  are 
frequently  employed  where  the  terra-cotta  block  lies 
snugly  against  a  metal  flange,  as  indicated  in  Fig.  59.  The 
many  possible  methods  which  may  be  employed  in  secur- 
ing proper  anchorage  cannot  always  be  shown  by  draw- 
ings, and  a  proper  execution  of  the  work  can  only  be 


Fig.  58. 


secured  by  most  careful  superintendence,  and  study  in  the 
field.  The  general  scheme,  however,  must  always  be  indi* 
cated  on  the  sprandrel  sections,  as  the  holes  necessary  in 
the  structural  metal-work  to  receive  the  anchors  should  be 
included  in  the  detail  drawings  of  the  iron  or  steel  work,  in 
order  that  such  punching  may  be  done  at  the  shop. 

Fig.  58  shows  a  sprandrel  section  from  the  Marquette 
Building,  at   the  fifteenth-floor  level.    Heavy  separators 


ARCHITECTURAL  ENGINEERING. 


SPANDRELS  AND  SPANDREL  SECTLONS.  107 


were  used  between  the  I-beam  girder  and  the  outside 
spandrel-channel. 

A  rather  complicated  spandrel  section  is  that  indicated 
in  Fig.  59,  taken  from  the  Marshall  Field  retail  store 
building.  The  spandrel-beams  were  here  carried  by  the 
masonry  piers  used  in  the  exterior  walls.  The  section 
shown  is  taken  where  small  ornamental  balconies  occur  in 
the  recessed  wall  between  the  piers.  The  vertical  mullion- 
angles  are  plainly  shown. 

Fig.  60  is  from  the  same  building,  taken  at  the  level 
where  the  granite  facing  stops  and  the  brick  and  terra- 
cotta work  begins. 

COURT  WALLS. 

The  spandrel  sections  of  the  court  walls  differ  in  no 
way,  as  far  as  general  principles  are 
concerned,  from  those  of  the  exterior 
walls.  They  are  generally  simpler, 
however,  due  to  the  plainer  character 
of  the  wall,  and  to  their  usual  de- 
crease in  thickness  as  compared  to 
the  exterior  walls.  A  glazed  brick  is 
commonly  employed,  to  reflect  all 
possible  light,  while  the  sill-courses, 
etc.,  are  of  terra-cotta  as  before. 

A  section  of  the  court  wall  in  the 
Marshall  Field  Building  is  given  in 
Fig.  61. 

A  simple  court-wall  spandrel  sec- 
tion is  shown  in  Fig.  62. 

BAY  WINDOWS. 

With  the  introduction  of  the  steel 
construction  came  the  possibility  and  demand  for  the  bay 


io8 


ARCHITECTURAL  ENGINEERING. 


window,  a  feature  which  has  certainly  become  very  promi- 
nent in  modern  office-building  and  hotel  design. 

As  in  the  ordinary  spandrel  section,  the  material  for 


X 

i 

&/oj'-  M  W*£i 

Fig.  62. — Typical  Court  Wall.    Practice  of  Jenney  &  Mundie,  Architects. 

each  story  must  be  carried  in  such  a  manner  as  to  make  it 
independent  of  the  other  stories.  This  is  accomplished  by 
means  of  brackets  at  each  floor  level,  and  in  order  that  the 
bracket  loads  may  not  become  too  heavy  the  bay-window 


SPANDRELS  AND  SPANDREL  SECTIONS. 


IO9 


walls  must  be  constructed  as  light  as  possible.  No  yielding 
or  deflection  is  permissible  in  these  brackets,  and  if  the 


Fig.  63. 


Fig.  64. 


supporting  member  is  a  floor-beam  or  floor-girder,  as  in 
Fig.  63,  taken   through  a  bay  window  of  the  Masonic 


I IO 


ARCHITECTURAL  ENGINEERING. 


Temple,  the  girder  should  be  rigidly  connected  to  the 
floor  system,  to  prevent  any  twisting  tendency  due  to  the 
weight  of  the  bay.    This  is  accomplished,  as  in  the  above- 


mentioned  figure,  by  means  of  the  top  and  bottom  tie- 
plates  shown. 

Fig.  64  shows  a  section  at  the  bottom  of  a  bay  window 
in  the  Masonic  Temple. 

Fig.  65  shows  a  half  plan  of  the  metal  framing  for  the 
State  Street  bay  window  in  the  Reliance  Building. 


112 


ARCHITECTURAL  ENGINEERING. 


The  terra-cotta  mullions  of  the  bay  and  the  pier  are 
shown  in  plan  in  Fig.  66. 

The  column  bracket  in  the  bay  is  given  in  Fig.  67,  while 
Fig.  68  is  a  section  at  the  side,  bracket. 

The  method  of  supporting  the  floors  and  ceilings  in  the 
bays  is  shown  in  Fig.  69. 


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£100*  L//1E 


2%.  Zs  .^ASS. 


6"^ 


^"x4x$  '2. 


jr  /z"x/j"Ts  /.8i 


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Fig.  69. 


5  ? 


-A.. 


CHAPTER  VII. 


COLUMNS. 

The  subject  of  the  interior  columns  forms  one  of  the 
most  important  steps  in  the  modern  problem  of  design,  and 
greater  variations  are  probably  to  be  found  here  than  in 
any  other  of  the  vital  features  in  iron  or  steel  construction. 
The  many  forms  of  columns  now  in  the  building  market, 
each  having  its  own  enthusiasts,  and  the  many  types  of 
connections  between  the  columns  themselves  and  with  the 
floor  system,  permit  ot  a  choice  from  a  dozen  or  more 
types,  with  the  details  varying  widely  in  each  case,  to  suit 
the  shape  chosen.  We  shall  endeavor  to  investigate  the 
more  prominent  forms,  and  point  out  the  advantages  and 
disadvantages  of  each  one.  The  most  satisfactory  for  gen- 
eral and  specific  cases  may  then  be  selected,  as  combining 
the  features  desired. 

A  discussion  as  to  the  relative  values  of  cast  versus 
wrought  columns  should  hardly  seem  necessary  at  the 
present  time,  but  the  repeated  use  of  the  cast-iron  column 
in  ten-  to  sixteen-storied  buildings,  and  even  higher  (as 
shown  by  their  use  in  the  new  Manhattan  Life  Insurance 
Building  of  seventeen  stories),  shows  that  the  questionable 
economy  of  cast  columns  does  still,  in  the  opinion  of  some 
architects,  compensate  for  the  dangers  incident  to  their 
use.  The  best  practice  has  declared  so  uniformly,  during 
the  last  few  years,  in  favor  of  the  steel  columns  that  the 
employment  of  cast  metal  is  new  pretty  generally  con- 
fined to  buildings  of  very  moderate  height  or  to  special 

113 


114 


ARCHITECTURAL  ENGINEERING. 


cases  where  advantages  are  to  be  gained,  as  in  the  use  of  a 
number  of  ornamental  cast  columns.  The  great  uncer- 
tainty as  to  the  uniformity  of  cast  metal  led  to  the  use  of  a 
very  low  unit-strain,  while  in  the  case  of  steel  the  unit- 
strains  can  be  assumed  on  a  very  definite  reliance  on  the 
trustworthiness  of  the  metal.  Among  our  more  progres- 
sive designers  the  use  of  cast-iron  in  large  buildings  has 
become  a  thing  of  the  past,  and  would  no  more  be  seriously 
considered  than  would  the  use  of  cast-iron  compression- 
members  in  bridges. 

Considering  the  cast  sections  in  more  general  use  as 
columns,  the  circular,  square,  and  H-shaped,  and  their  indi- 
vidual connections  (see  Fig.  70),  it  will  be  seen  that  these 

splices  cannot  result  in  as  rigid 
a  framework  as  the  riveted 
joints  in  steel-work.  The  col- 
umns in  the  modern  design 
must  be  capable  of  affording 
stiff  connections  so  as  to  with- 
stand both  the  direct  dead 
and  live  loads  transferred  from 
the  floor  system,  as  Avell  as 
sufficient  connections  for  the 
wind  bracing.  These  cannot 
be  secured  well  by  means  of 
bolts  passing  through  the  horizontal  flanges  of  cast  columns, 
even  if  the  workmanship  be  considered  accurate.  The 
workmanship,  however,  can  seldom,  if  ever,  be  relied 
upon  as  perfect ;  the  bolts  never  completely  fill  their 
holes,  and  "  shims  "  are  constantly  employed  to  plumb  the 
columns.  These  constitute  elements  of  weakness  which 
may  easily  allow  considerable  distortion.  The  girder 
connections  to  the  columns,  resting  on  cast  brackets,  and 
bolted  through  the  flanges,  are  bad  in  the  extreme,  espe- 


7  f 


Fig.  70. 


/ 


COL  UMNS.  1 1 5 

cially  for  cases  of  eccentric  loading  and  the  irregular  plac- 
ing of  beams. 

To  offset  these  dangers  of  weak  design  it  is  true  that 
cast  columns  are  cheaper  per  pound  and  perhaps  easier  of 
erection  than  the  steel — considerations  that  naturally  have 
much  weight  with  the  owner  of  the  building.  But  consider- 
ing the  risks  that  are  run,  as  in  the  building  at  14  Maiden 
Lane,  New  York,  which  was  blown  eleven  inches  out 
of  plumb  through  the  inability  of  the  cast  columns  to  resist 
the  wind  pressure,  it  is  hard  to  understand  why  architects 
will  persist  in  the  use  of  such  methods,  even  if  requested 
by  the  owner.  Cast  iron,  in  spite  of  its  apparent  stiffness, 
has  a  much  lower  coefficient  of  elasticity  than  steel,  break- 
ing suddenly  when  it  breaks,  while  steel  suffers  distortion. 

Steel  is  now  being  rolled  at  such  a  low  price  that,  con- 
sidering the  extra  weight  necessary  in  cast  iron,  on  account 
of  its  unreliability,  the  saving  in  cost  by  the  use  of  the 
latter  will  be  found  to  be  small  indeed,  even  disregarding 
the  dangers  assumed  by  its  use. 

The  more  prominent  forms  of  American  wrought 
columns  include  the  Phoenix,  Keystone  octagonal,  latticed 
angles,  channels  and  lattice,  plates  and  angles,  Z-bar 
columns,  and  the  newer  Larimer  and  Gray  types.  The 
relative  advantages  of  these  various  sections  are  of  the 
greatest  importance,  as  affecting  economical  and  successful 
design.  In  actual  practice  the  treatment  of  these  different 
shapes  will  be  found  to  vary  greatly  with  the  designer — 
not  only  in  the  relative  value  of  the  sections,  but  in  the 
treatment  of  any  one  section.  In  the  first  place,  the 
formulas  differ  greatly,  not  in  fundamental  principles,  per- 
haps, but  in  the  treatment,  being  often  empirical,  and  con- 
taining factors  deduced  from  some  special  case.  These 
formulae  also  generally  assume  ideal  loading,  which  will 
seldom  occur  in  the  modern  building,  and  no  or  very  few 


n6 


A  R  CHI  TECT  URA  L  ENGIA  ^  EE  RISK  TG . 


full-sized  tests  have  ever  been  made  on  the  effects  of  eccen- 
tric loading.  Indeed,  the  full-sized  tests  on  columns  of 
concentric  loads  even,  have  been  far  too  limited  to  show 
the  relative  values  of  the  most  ordinary  column  sections. 

Burr,  in  his  "  Strength  and  Resistance  of  Materials,'' 
states  that  "  The  general  principles  which  govern  the  re- 
sistance of  built  columns  may  be  summed  up  as  follows  : 

"  The  material  should  be  disposed  as  far  as  possible  from 
the  neutral  axis  of  the  cross-section,  thereby  increasing  R  ; 

"  There  should  be  no  initial  internal  stress ; 

"  The  individual  portions  of  the  column  should  be 
mutually  supporting ; 

"  The  individual  portions  of  the  column  should  be  so 
firmly  secured  to  each  other  that  no  relative  motion  can 
take  place,  in  order  that  the  column  may  fail  as  a  whole, 
thus  maintaining  the  original  value  of  R." 

The  experiments  given  by  Burr  would  seem  to  indicate 
that  a  closed  column  is  stronger  than  an  open  one,  due  to 
the  fact  that  the  edges  of  the  segments  are  mutually  sup- 
porting when  held  in  contact  by  complete  closure.  From 
a  theoretical  standpoint,  therefore,  the  Phcenix  column  is 
undoubtedly  the  most  favorable  form  for  compression,  as 
it  forms  a  closed,  and  thus  mutually  supporting,  section  ; 
and  because  the  capacity  of  columns  of  equal  areas  varies 
as  the  metal  is  removed  from  the  neutral  axis.  It  must  also 
be  remembered  that  any  form  of  column,  having  a  maxi- 
mum and  minimum  radius  of  gyration,  is  not  economical 
for  use  under  a  single  concentric  load,  as  the  calculations 
must  be  based  on  the  minimum  radius  of  gyration.  The 
metal  represented  by  the  excess  of  the  maximum  radius  of 
gyration  is  of  necessity  disregarded,  and  part  of  the  section 
is  thus  lost  or  wasted,  when  we  consider  the  ideal  efficiency 
of  the  column.  But  practice  does  not  always  support 
theory,  and  many  other  questions  besides  mere  form  arise 


COL  UMNS.  I  1 7 

in  connection  with  the  judicious  choice  of  a  section.  In- 
deed, we  shali  see  that  several  practical  considerations  in 
the  use  of  columns  in  buildings  call  for  a  form  very  differ- 
ent from  the  ideal  circular  section  ;  such  points*  as  the 
transfer  of  loads  to  the  centre  of  the  section,  the  maximum 
efficiency  under  eccentric  loading,  and  the  requirements 
for  pipe-space  around  or  included  in  the  column  form,  all 
tend  seriously  to  restrict  the  use  of  closed  or  circular 
sections. 

In  the  column  formula,/)  =  ~   (the  form 

of  Gordon's  formula,  including  the  effect  of  eccentric 
loading),  there  are  expressions  for  the  three  kinds  of 
stresses  in  a  column  under  compression — that  due  to  the 
flexure  of  the  column,  that  clue  to  eccentric  loading,  and 
that  due  to  the  uniformly  distributed  load.  The  term  of 
eccentric  loading  does  not  occur  in  the  so-called  Gordon's 
formula,  or  in  those  derived  from  it,  but  in  building  con- 
struction this  term  must  not  be  omitted.  The  placing  of 
columns  centrally  over  one  another  necessitates  the  applica- 
tions of  loads  to  the  sides  of  the  columns,  and  unless  the 
loads  are  equal,  and  on  opposite  sides  of  the  column,  the 
effect  is  to  increase  the  stress  on  the  side  where  the  greater 
load  occurs. 

P 

The  second  term  in  the  denominator,  a  — ,  is  usually  so 

r 

small  that  it  really  makes  this  term  of  the  least  importance 
in  the  above  equation,  due  to  the  ordinarily  short  length  of 
columns  in  buildings,  and  to  their  usual  broad  flat  bases. 
Hence  in  one-story  columns  (unless  in  long  first-story  col- 
umns), where  the  length  is  usually  under  90  radii,  the  differ- 
ence in  the  strength  of  the  various  sections  tends  to  disap- 
pear, and  almost  any  of  the  sections  will  answer  with  the 


u8 


ARCHITECTURAL  ENGINEERING. 


ordinary  unit-strains,  if  the  columns  are  well  made  and  the 
loads  are  not  eccentric.  Eccentric  loading  will  be  consid- 
ered later,  under  a  general  discussion  of  the  various 
sections. 

In  longer  columns,  however,  where  the  length  is  greater 
than  90  radii,  calculation  by  the  radius  of  gyration  becomes 
necessary.  In  the  new  Schiller  Theatre  Building,  Chicago, 
Phoenix  columns  were  used,  of  a  length  of  92  ft.  10  in., 
weighing  25,000  lbs.  each.  Modern  building  methods  have 
rapidly  developed  the  necessity  for  columns  of  extraordinary 
length,  carrying  loads  hitherto  considered  visionary.  It  is 
not  uncommon  to  have  800  tons  and  even  more  on  a  single 
column  with  a  sectional  area  of  158  sq.  in.  The  Edison 
Electric  Illuminating  Company  of  New  York  City  used 
columns  of  the  Phoenix  type,  having  loads  of  600  net  tons, 
35  ft.  4  in.  over  all  in  length,  weighing  15,000  lbs.  each.  As 
vibration  occurred  in  the  building,  very  low  unit-strains 
were  allowed,  the  columns  being  further  strengthened  by 
disregarding  the  increment  to  the  least  radius  of  gyration 
caused  by  using  eight  fillers,  each  \\  in.  thick. 

The  formula  used  was  one  deduced  from  the  experi- 

,    t  t  t                                 1    P  42'000 
ments  at  the  Watertown  Arsenal, namely,  -~.  =  


for  the  crushing  strain  per  sq.  in. 

Twelve-section  Phoenix  columns  were  also  used  in  the 
Chicago  Board  of  Trade,  90  ft.  unsupported  length,  3  ft. 
3  in.  diameter,  fire-proofed. 

But  by  far  the  larger  number  of  columns  used  in  modern 
building  construction  are,  as  has  before  been  stated,  under 
90  radii,  being  used  in  single-story  lengths  of  from  10  to  14 
feet.  The  determining  factors  are,  therefore,  such  practical 
considerations  as  affect  columns  of  these  lengths;  so  that 
the  ideal  disposition  of  the  metal  must  be  considered  in  con- 


COL  UMNS. 


HQ 


nection  with  other  very  important  requirements.  The  fol- 
lowing points  of  the  problem  are  important,  in  a  discussion 
of  which  the  writer  partly  follows  the  points  enumerated  by 
Mr.  C.  T.  Purdy,  in  the  Engineering  News,  December  5,  1891: 

1.  Cost,  availability. 

2.  Shopwork,  and  workmanship  of  column. 

3.  Ability  to  transfer  loads  to  centre  of  column — eccen- 
tric loading. 

4.  Convenient  connections  of  floor  system. 

5.  Relation  of  size  of  section  to  small  columns. 

6.  Fire-proofing  capabilities  of  the  section. 

Points  1  and  2  are  of  the  greatest  importance  to  the 
owner  and  builder,  and  often  govern  the  selection  of  the 
column.  Points  3,  4,  and  5  are  for  the  engineer's  considera- 
tion, while  point  6  is  of  chief  interest  to  the  architect  and 
decorator. 

1.  Cost,  Availability. — The  question  of  the  cost  of  the 
material  as  it  comes  from  the  mill  is  a  purely  commercial  one, 
depending  upon  the  market  price  per  pound  of  the  section 
used.  The  break  in  the  combine  which  formerly  existed  on 
I  beams  and  channels  has  reduced  the  price  on  these  sections 
from  the  former  combine  price  of  $3.20  to  about  $1.50,  or  to 
a  price  uniform  with  that  for  plates  and  angles.  Indeed  the 
price  of  iron  and  steel  shapes  has  never  been  so  low  in  the 
history  of  this  country  as  at  the  present  time,  and  were  such 
prices  to  continue,  they  would  doubtless  prove  a  tremendous 
stimulus  to  steel  construction  even  in  dwellings. 

All  of  the-  "  patent  "  columns,  such  as  Z-bar,  Phoenix, 
Keystone  octagonal,  Larimer,  and  Gray  forms,  have  the 
great  disadvantage  of  being  rolled  or  manufactured  by  cer- 
tain mills  only,  and  in  this  age  of  push  and  hurry  the  quick 
delivery  of  material  is  a  very  essential  point.  The  demands 
for  structural  steel  at  good  seasons  of  trade  in  this  country, 
are  so  great  that  it  is  next  to  impossible  to  secure  such  a 


120 


ARCHITECTURAL  ENGINEERING. 


prompt  delivery  of  material  as  is  required  for  the  comple- 
tion of  a  large  building-  within  the  contract  time.  The  con-  ' 
tracts  that  have  been  executed  in  the  city  of  Chicago  dur- 
ing the  last  three  or  four  years  have  undoubtedly  shown 
the  most  wonderful  construction  in  points  of  excellence  and 
time  that  the  world  has  ever  seen ;  while  it  is  said  of  a  large 
building  in  New  York  City  that  the  masonry  for  the 
twelfth  story  was  laid  before  the  mortar  at  the  first-floor 
level  was  dry.  The  patent  on  the  more  important  of  the 
patent  sections  has,  however,  recently  expired,  so  that  now 
the  Z  section  is  being  rolled  by  several  mills,  and  it  is  not 
only  cheaper  than  formerly,  but  much  more  available, 
being  rolled  even  on  the  Pacific  coast.  The  Phoenix  shape, 
although  the  patent  has  long  since  expired,  is  rolled  by  but 
one  mill  in  this  country,  the  Phcenixville,  and  by  one  other 
mill  in  England.  The  Keystone  column  is  but  little  used. 
Columns  of  plates  and  angles,  or  channels,  possess  this  ad- 
vantage of  availability  in  a  greater  measure  than  any  of  the 
other  sections,  the  parts  being  obtainable  at  any  mill,  if  not 
in  stock. 

2.  Shopwork  and  Workmanship. — With  the  present  uni- 
form low  price  per  pound  of  most  of  the  column  sections, 
the  items  of  shopwork  and  workmanship  become  of  far 
greater  importance  in  the  cost  of  the  completed  column 
than  the  cost  of  the  section  at  the  mill — assuming  the  sec- 
tional area,  and  hence  the  weight  per  foot,  to  be  the  same. 
Lattice  bars,  fillers,  gussets,  etc.,  add  just  so  much  more 
weight,  without  increasing  the  section,  and  must  there- 
fore be  considered  from  an  economical  standpoint.  The 
methods  of  riveting  the  sections  together  in  the  various 
forms  must  also  be  taken  into  account. 

The  number  of  punching  operations,  as  well  as  the  ex- 
pense of  rolling  the  sections  employed,  will  need  to  be  con- 
sidered as  affecting  the  cost  of  shopwork.     Thus  in  the 


COLUMNS.  121 

Gray  column  no  less  than  sixteen  operations  of  punching 
are  required  for  four  rows  of  rivets,  with  the  additional 
expense  of  hydraulic  pressed  bent  plates,  connecting  the 
angles.  This  will  materially  increase  the  cost  of  manufac- 
ture.   (See  following  table.) 

Larimer  column,  i  row  of  rivets. 


I 


Z-bar  column,  without  covers,  2  rows. 
^   4-section  Phoenix  column,  4  rows. 


4 — s 


Channel  column,  with  plates  or  lattice,  4  rows. 

Gray  column,  4  rows. 

Keystone  octagonal  column,  4  rows. 

Z-bar  column,  with  single  covers,  6  rows. 

Box  column  of  plates  and  angles,  8  rows. 

Latticed  angle  column,  8  rows. 

8-section  Phoenix  column,  8  rows. 

Z-bar  column  with  double  covers,  10  rows. 


The  new  Larimer  column,  but  recently  placed  on  the 
market  by  Jones  &  Laughlins,  and  first  used  in  Chicago 
in  the  Newberry  Library  building,  consists  of  two  I-beam 
sections  bent  down  along  the  middle  of  the  web,  the 
two  beams  being  riveted  together  with  a  small  I-beam 
filler  between.  The  rivets  are  spaced  3  in.  centres  for 
about  18  in.  from  each  end  of  the  column,  and  then  5  in. 
centres. 


122 


A  R  CHI  TECTURA  L  ENG  IN  EE  RING. 


Where  necessary  to  strengthen  the  column,  this  filler  is 
made  of  two  channel-sections,  back  to  back,  extending  out  on 
either  side  as  far  as  necessary.  Small  angles  are  riveted  to 
the  faces  of  the  I  beams,  and  a  plate  is  riveted  across  the  top, 
on  which  the  girders  and  column  rest  (Fig.  71).  Where 


Fig.  71, 


Fig.  72. 


only  two  girders  occur,  the  remaining  faces  are  used  to 
rivet  the  upper  column  to  the  plate.  Another  method  has 
been  used  instead  of  the  small  angles,  in  the  shape  of  a 
square  or  octagonal  sheet  which  is  cut  from  the  centre 
out,  part  way  to  the  edge,  and  the  lips  so  formed  are  bent 
down  in  a  press,  thus  making  a  solid  and  continuous  angle. 
Still  another  detail  has  been  made  by  pressing  out  in  a 
hydraulic  machine  a  circular  sheet  to  conform  in  the  lower 
part  to  the  shape  of  the  outside  of  the  flanges  of  the  column 
(Fig.  72).  In  this  way  not  only  the  upper  flange,  but  the 
vertical  flange  too,  is  made  continuous  around  the  top  of 
the  column.  Also  the  thickness  of  the  horizontal  flange  is 
retained  uniform,  the  thickness  of  the  vertical  flange  being 
somewhat  tapered. 

This  column  is  one  of  the  cheapest  on  the  market  at  the 
present  time,  but  it  possesses  one  great  disadvantage  in  the 
smaller  sized  columns.  This  lies  in  the  difficulty  of  driving 
the  rivets  that  connect  the  bracket  angles  with  the  I-beam 
flanges.  In  a  o-in.  column,  where  5-in.  I  beams  are  used,  or 
in  smaller  columns,  it  is  often  very  difficult  on  account  of 


COL  UMNS. 


123 


interference  to  drive  the  rivets  through  the  holes,  unless  the 
rivets  are  driven  in  a  slanting  direction.  This  often  re- 
sults in  weak  connections.  Jones  &  Laughlins,  the  manufact- 
urers of  this  column,  have  made  a  large  number  of  tests  of 
built  columns,  showing  a  marked  gain  in  ultimate  strength 
over  the  Z-bar  column  tests  published  by  C.  L.  Strobel. 
Comparing  a  7"  Larimer  column  (6"  I  beams,  I2|  lbs.  per 
foot,  of  sectional  area  of  9.261  □  ",  total  length  120",  gauged 
length  100")  with  a  6"  Z-bar  column  (6"  X  3"  Z's,  \"  metal, 
area  =  9.32  □  ",  total  length  =  1 19.88",  gauged  length  =  80"), 
the  Larimer  shows  an  ultimate  strength  of  346,300  lbs.,  or 
37,393  lbs.  per  sq.  in.,  as  compared  with  an  ultimate 
strength  of  293,200  lbs.,  or  31,460  lbs.  per  sq.  in.  for  the  Z 
column.  The  Z-bar  column  failed  through  the  buckling  of 
the  Z's,  and  twisted  in  a  spiral  direction  between  the  two 
ends.  The  Larimer  column  deflected  in  an  oblique  direc- 
tion. Larger  Larimer  columns  also  showed  a  greater  ulti- 
mate strength  per  sq.  in.  than  the  Z-bar  columns. 

A  point  that  has  always  been  made  much  of  in  the 
claims  for  the  Z-bar  column  is  that  but  two  rows  of  rivets 
are  required,  and  those  near  the  centre  of  the  column  ;  for 
it  is  reasonable  to  suppose  that  punching  in  the  outer  por- 
tions of  a  column  tends  to  weaken  the  member,  even  when 
the  riveting  is  most  carefully  done  ;  and  this  is  even  more 
important  in  small  columns,  where  the  ratio  of  the  radius  of 
gyration  to  the  length  of  the  column  is  greatest,  and  where 
we  desire  the  greatest  efficiency  of  the  material  used.  But 
is  this  claim  of  two  rows  of  rivets  founded  on  fact  ?  If  Z-bar 
columns  were  used  without  cover-plates,  the  claim  w^ould 
indeed  be  true,  but  take,  for  instance,  the  large  Z-bar  col- 
umns in  the  Venetian  Building,  quoted  by  Mr.  Purdy  in  the 
article  named.  No  less  than  ten  rows  of  rivets  are  required 
with  the  heavy  cover-plates  used,  and,  indeed,  when  we 
stop  to  consider  the  large  proportion  of  Z-bar  columns 


124  ARCHITECTURAL  ENGINEERING. 

which  "have  covers,  the  claim  of  only  two  rows  of  rivets 
assumes  but  little  value,  and  the  section  proves  less  desira- 
ble than  the  box  column  of  plates  and  angles, — inasmuch 
as  the  material  of  the  Z's,  near  the  centre  of  the  column,  is 
practically  wasted,  though  adding  so  materially  to  the 
weight.  It  can  hardly  be  denied,  even  by  the  most  enthu- 
siastic supporters  of  the  Z  section,  that  the  use  of  this  shape 
has  really  been  thrust  upon  the  Chicago  builders  during 
the  last  few  years  far  more  than  its  merits  would  warrant. 
A  glance  at  the  Appendix  table  shows  that  twenty-two  out 
of  a  total  of  forty  buildings  in  Chicago  have  used  the  Z- 
bar  column.  Its  use  in  Eastern  cities  has  been  far  more 
limited. 

It  is  hard  to  see,  therefore,  where  the  Z-bar  column 
possesses  any  decided  advantage  so  far  as  shopwork  is  con- 
cerned, unless  used  without  cover-plates.  The  columns  of 
plates  and  angles  and  the  Z  sections  are  about  on  a  par  in 
these  respects,  while  the  channel  columns  are  more  favora- 
ble than  either.  The  channel  columns  are,  however,  some- 
what limited  as  to  section,  while  plates  and  angles  can  be 
increased  to  any  desired  area.  The  latter  section  was  used 
in  the  highest  steel  building  in  Chicago,  the  Masonic  Tem- 
ple, latticing  being  used  on  two  sides  of  the  columns  in  the 
upper  stories. 

The  character  of  workmanship  will  vary  with  the  differ- 
ent shops,  as  wreli  as  with  the  different  sections  used.  The 
reputation  of  the  shop,  aided  by  careful  inspection,  will  de- 
termine the  excellence  of  the  workmanship. 

3.  Ability  to  Transfer  Loads  to  Centre  of  Column — Eccen- 
tric Loading.— -It  will  be  seen  at  a  glance  that  many  of  the 
sections  under  consideration  are  totally  unfitted  for  the 
transfer  of  loads  to  the  centre  of  the  column.  The  condi- 
tions in  designing  a  framework  are  seldom  so  favorable  as 
not  to  require  many  of  the  columns  to  be  loaded  unsym- 


) 


COL  UMNS. 


125 


metrically,  and  this  point  has  been  carefully  considered  in 
the  details  of  the  best  modern  structures,  in  order  to  obtain 
the  highest  possible  efficiency  in  the  material  used.  Every 
step  in  this  direction  will  certainly  add  to  the  capacity  of 
the  column,  for  an  eccentric  load  will  necessitate  the  use  of 
a  much  less  mean  unit-strain  than  where  the  force  can  be 
applied  directly  to  the  axis.    Fig.  73  shows  the  connection 

between  beams  or  girders  and 
the  Gray  column.  It  is  evi- 
dent that,  unless  the  top  of  the 
column  is  very  rigidly  bound 


G  • 


OOO 


• 

• 

0 

0 

• 

0 

• 

0 

G 

• 

• 

0 

0 

• 

O  OOP 


   ± 

Fig.  73.  Fig.  74. 

together  by  outside  plates  or  angles,  the  girder  loads,  if 
eccentric,  are  borne  mainly  by  the  T  shape  to  which  the 
girder  is  connected,  and  not  by  the  whole  column.  Thus 
lack  of  latticing  to  transmit  shear  may  constitute  a  very 
serious  disadvantage  in  cases  of  heavy  eccentric  loading. 

The  use  of  Phoenix  plates  with  pintle  connections,  as 
advocated  by  Foster  Milhken,  would  certainly  seem  to 


126 


ARCHITECTURAL  ENGINEERING. 


possess  the  greatest  advantages  under  this  heading  (Fig. 
74).  There  is  no  leverage  in  this  method  to  tear  the  joint 
asunder,  as  there  is  in  any  fiange  joint.  This  system  was 
recently  used  in  the  large  power-house  of  the  Broadway 
cable  road  in  New  York,  with  pintle-plates  over  eight  feet 
deep.  Unless  pintle-plates  can  be  used,  however,  any  form 
of  closed  column  is  bad  under  this  consideration  of  central 
loads,  and  here  the  practical  method  of  loading  columns 
conflicts  seriously  with  the  use  of  an  ideal  closed  section. 

The  Z-bar  column  possesses  advantages  here,  too,  over 
most  of  the  forms  of  closed  columns,  and  even  when  cover- 
plates  are  used  this  is  so  (though  not  in  as  great  a  degree), 
as  the  column  may  almost  always  be  turned  so  that  the 
heavily  loaded  beam  may  be  introduced  between  the  Z 
flanges.  This  advantage  is  especially  great  at  the  tops  of 
buildings  where  small  columns  without  cover-plates  carry 
beams  with  heavy  loads,  for  here  the  column  is  open  on 
all  four  sides,  so  that  all  loads  may  be  taken  to  the  centre 
of  the  column.  (But  Z-bar  columns  without  covers  fail  by 
wrinkling,  and  under  this  condition  they  are  the  weakest 
of  any  of  the  sections.)  The  box  column  of  plates  and 
angles,  however,  possesses  this  same  advantage,  though  not 
to  as  great  an  extent  in  the  lighter  sections.  The  possi- 
bility of  changing  the  section  of  a  column  so  that  the 
radius  of  gyration  shall  be  greater  or  less  in  either  direc- 
tion across  the  section  must  not  be  overlooked,  for  if  all  the 
loads  occur  on  one  side  of  a  column,  it  is  a  great  advantage 
to  have  the  radius  of  gyration  greater  in  the  line  of  the 
load. 

The  calculation  for  eccentric  loading  should  be  treated  a 
follows  : 

(a)  Determine  the  section  required  for  the  total  load,  both 
eccentric  and  concentric,  the  whole  considered  as  concen- 
tric. 


COL  UMNS. 


127 


{b)  Find  yv  or  half  the  width  of  the  column. 

(c)  Find  the  radius  of  gyration  in  the  plane  of  eccentric 
loading. 

(d)  Find  the  area  of  section  required  to  resist  the 
bending  moment  arising  from  the  eccentric  loading,  using 
radius  of  gyration  and  yx  as  in  the  assumed  section.  The 
moment  due  to  eccentric  loading  will  equal  the  eccentric 
load  X  its  distance  of  application  from  the  axis  of  column,  or 


M«yx 


f1     fAr*  1 

:  —  =   ,  whence    A  =  — 


o 


(e)  If  this  second  area  can  be  added  to  the  first  assumed 
area  of  section  without  changing  the  radius  of  gyration  and 
yx  materially,  it  may  be  done,  thus  obtaining  the  total  area 
of  section  without  a  new  solution. 

(/)  If,  however,  the  radius  of  gyration  andjy,  are  changed 
materially,  in  providing  for  the  new  area  required,  then 
a  new  assumed  sectional  area  is 
taken,  radius  of  gyration  and  yx 
found  for  it,  the  solution  proceed- 
ing as  before. 

4.  Convenient  Connections. — This 
feature  in  column  construction  is 
a  very  important  one.  Satisfac- 
tory details  can  easily  be  made 
for  almost  any  of  the  sections, 
where  the  beams  are  symmetri- 
cally placed  and  loaded,  and  where 
all  occur  at  the  same  elevation  ; 
but  when  the  irregular  placing 
of  beams  is  necessitated,  as  re- 
gards position,  load,  and  height, 
it  is  important  that  the  character  of  the  column  afford 
as  great  an  opportunity  as  possible  for  the  connection  of 


Fig.  75. 


128  ARCHITECTURAL  ENGINEERING. 

plates  and  angles.  The  connection  in  Z-bar  columns  forms 
one  of  the  greatest  advantages  in  the  use  of  this  section ; 
and  in  the  smaller  columns  without  covers,  where  the  con- 
nections are  generally  the  most  difficult,  the  advantages 
are  the  greatest.  The  general  system  of  connections  is 
shown  in  Fig.  75,  taken  from  the  Monadnock  Building. 

Angle-brackets  are  riveted  to  the  column,  on  which  is 
placed  a  plate  \  in.  to  1  in.  in  thickness,  on  top  of  which  come 
the  girders,  the  column  of  the  next  floor  setting  centrally 
over  the  one  below.  The  girders  are  riveted  or  bolted 
through  to  the  bed-plate  below,  by  the  flanges,  and  through 
an  angle  above,  as  shown  in  Fig.  75.  A  small  wrought-iron 
"  gib "  or  wedge  is  dropped  in  between  the  top  end  of 
the  girder  and  the  web,  to  take  up  any  possible  compressive 
strains.  If  the  girders  are  all  to  be  brought  to  one  level, 
cast-iron  bolsters  are  used. 

The  system  followed  in  the  Phoenix  column  is  as  shown 
in  Fig.  76,  consisting  of  angles  riveted  to  the  extended 
fillers,  on  which  a  plate  is  placed, 
holding  the  girders  and  the  super- 
imposed column.  The  upper  column 
is  held  down  by  angles  riveted  to 
the  bed-plate.  Under  eccentric  load- 
ing a  considerable  tilting  movement 
occurs  in  this  column,  unless  used 
with  pintle-plates,  as  before  sug- 
gested. Connections  were  made  with  bent  plates  in  the 
Old  Colony  Building,  Chicago,  as  shown  in  Fig.  77. 

Box  columns  of  plates  and  angles  offer  quite  as  many 
advantages  as  regards  connections,  if  not  more,  than  any 
other  section.  The  details  are  really  the  simplest  of  all, 
when  we  consider  columns  of  a  single  floor  height  only 
(Fig.  78),  but  the  joint  is  not  a  desirable  one,  nor  is  any  where 
a  horizontal  plate  separates  the  two  columns  ;  for  it  prevents 


COL  UMNS  1 29 


efficient  splicing,  as  well  as  good  girder-connections.  This 
point  will  be  taken  up  later  under  the  head  of  "  Column 
Joints." 


Fig.  77. 


5.  Relation  of  Size  of  Section  to  Small  Columns. — It  is  not 
generally  desirable  in  building  construction  to  have  a  very 
small  column  in  the  upper  stories,  because  girder  loads  are  so 
much  heavier,  proportionately,  than  the  column  loads.  Some- 
times as  many  as  six  beams  must  connect  with  an  upper- 
story  column  at  one  level,  and  in  such  cases  it  is  almost 
impossible  to  make  good  connections  with  a  small  column. 

6.  Fire-proo fing  Capabilities  of  the  Section. — T  h  e  rectangu  lar 
column  sections  will  not,  oi  course,  fire-prool  as  compactly 
as  the  circular  sections,  but  when  the  room  thus  lost  is 
used  for  "  pipe-space,"  as  is  becoming  more  and  more  fre- 
quent, this  point  has  great  value  in  the  estimation  of 
architects.  In  the  Columbus  Building,  Chicago  (1893),  a 
square  hole  was  cut  in  all  of  the  bed-plates  of  the  columns 
to  allow  the  passage  of  pipes  inside  of  the  column  area. 
Such  a  cutting  of  bed-plates  cannot  be  too  severely  con- 
demned. The  increased  use,  however,  of  vertical  splices 
in  columns,  instead  of  horizontal  bed-  and  cap-plates,  allows 
all  water-,  waste-,  and  vent-pipes  to  be  carried  up  along  the 
side  of  the  metal  columns,  and  inside  the  fire-proofing  slabs, 


130 


ARCHITECTURAL  ENGINEERING. 


where  the  room  may  be  had  without  too  much  waste.  It 
is  not  advisable  to  place  any  piping  inside  of  the  metal 
columns,  and  hence  such  sections  as  the  Phcenix  and  Key- 
stone-octagonal offer  no  advantages  in  this  respect.  The 
columns  of  plates  and  angles,  channels,  Z's  and  the  Gray 
column,  all  allow  considerable  pipe-space  within  the  mini- 
mum circular  or  rectangular  enclosure  for  fire-proofing. 

It  would  seem,  however,  that  separate  ducts  in  the 
walls,  or  along  the  sides  of  the  columns  for  all  piping 
would  be  far  better  than  such  concealed  risers.  Separate 
ducts  would  result  in  increased  outlay,  but  they  would 
offer  the  great  advantage  of  allowing  inspection  of  all 
piping  whenever  and  wherever  desired. 

The  largest  Z-column  section  in  "The  Fair"  building, 
Chicago,  consists  of  4  Z  bars  6"  X  J",  2  webs  16"  X  f " ,  6 


plates  26"  X  4  angles  4"  X  4"  X  |f",  4  angles  5"  X  4" 
x  7"  _  total  =  218  sq.  in.  The  minimum  Z  section  gener- 
ally used  is  4  Z's  3"  X  A",  I  web  8"  X  TV  =  12.4  sq.  in. 
Metal  less  than  T5¥"  in  thickness  is  never  used  in  the  best 
practice. 

The  calculations  of  the  strengths  of  wrought  columns, 
in  accordance  with  the  building  laws  of  New  York,  Boston, 
and  Chicago,  are  given  in  Chapter  XII;  and  the  unit- 
strains  used  in  several  prominent  buildings  are  given  in 
Chapter  XI. 

It  is  apparent,  therefore,  that   each  of  the  types  of 


Fig.  79. 


covers  16"  X  ,  aggregating  an  area 
of  142  sq.  in.  and  carrying  a  load  of 
1,700,000  lbs.  The  largest  Z  column  in 
the  new  Y.  M.  C.  A.  Building,  Chicago 
(see  Fig.  79),  was  a  two-story  column 
24'  3"  long,  composed  as  follows:  4  Z's 
6"  X  3"  X  r>  2  plates  24"  X  J">  2 
plates   16"  X  |",  1  plate    14"  X  f"  2 


COL  UMNS.  1 3 1 

columns  considered,  has  its  own  good  points,  but  the  choice 
of  one,  as  decidedly  superior  to  all  others,  would  be  well- 
nigh  impossible.  The  Larimer  column  may  lead  in  cheap- 
ness, the  Z  or  box  columns  are  superior  for  connections, 
the  material  in  the  Phcenix  or  Keystone  columns  is  placed 
most  advantageously  from  a  theoretical  standpoint.  The 
choice,  then,  must  depend  on  the  personal  views  of  the  de- 
signer, as  well  as  on  the  local  conditions  as  to  cost,  manu- 
facture, and  the  details  employed  in  the  problem  at  hand. 
The  writer  favors  the  box  column  of  plates  and  angles.  It 
is  easily  obtained,  cheap,  good  for  connections,  possesses  a 
minimum  and  maximum  radius  of  gyration,  which  can  be 
utilized  under  eccentric  loading,  and  it  offers  the  greatest 
advantages  for  continuous  columns,  a  point  which  will  be 
considered  later  in  connection  with  wind  bracing. 

A  discussion  on  columns  would  hardly  be  complete 
without  some  reference  to  the  views  expressed  on  this  sub- 
ject by  Gen.  Wm.  Sooysmith.  He  advises  the  use  of 
limestone  pillars  instead  of  steel  columns,  declaring  that  the 
action  of  the  metal-work  under  heat  would  be  dangerous  in 
the  extreme.  To  quote  :  "  There  may  be  steel  buildings  in 
which  the  fire-proofing  has  been  so  well  done  that  they  will 
pass  through  an  ordinary  fire  without  such  failure.  But  if 
the  steel  becomes  even  moderately  heated,  its  stiffness  will 
be  measurably  diminished,  and  the  strength  of  the  upright 
members  so  reduced  as  to  cause  them  to  bend  and  yield/* 
While  acknowledging  the  great  experience  and  ability  of 
Gen.  Sooysmith  in  constructive  work,  and  especially  in  foun- 
dations, the  writer  would  seriously  question  the  authority 
for  such  an  apparent  reflection  on  fire-proofing  methods. 
There  not  only  may  be  buildings  which  are  sufficiently  fire- 
proofed,  but  it  is  a  well-established  fact  that  builders,  archi- 
tects, and  engineers  can  and  do  fire-proof  their  buildings 
sufficiently  to  guard  against  all  possible  heat  arising  from 


132  ARCHITECTURAL  ENGINEERING. 

the  material  used  in  the  building,  or  from  the  burning  of 
surrounding  structures.  And  that  there  is  almost  no  limit 
to  the  possibility  of  protection  from  heat  by  fire-clay  is 
shown  in  the  immense  converters  in  use  by  the  large  steel 
companies.  They  are  made  of  steel,  protected  by  fire-clay, 
and  in  spite  of  a  temperature  of  20000  night  and  day,  these 
furnaces  last  even  as  long  as  four  years  before  renewal. 

Again,  limestone  (CaCo3)  is  friable  under  the  action  of 
heat,  decomposing  into  lime  (CaO)  and  carbon  di-oxide 
(CO,)  at  a  temperature  of  6oo°.  Hence  the  limestone  pillars 
would  require  quite  as  much  protection  by  fire-proofing 
as  the  steelwork.  Gen.  Sooysmith  claims  a  safe  load  of  500 
tons  for  a  column  of  limestone  21  X  2'  in  area  and  9/  high. 
This  equals  576  sq.  in.,  or  at  5500  lbs.  per  sq.  in.  given  by 
Rankine,  gives  an  ultimate  compressive  resistance  of  1584 
tons.  Allowing  the  factor  of  safety  of  8,  recommended  by 
Rankine,  we  have  even  less  than  200  tons,  while  Baker 
recommends  but  20  or  25  tons  per  sq.  ft.  for  the  best 
ashlar  masonry  (10  tons  was  the  maximum  pressure  in  the 
Brooklyn  bridge,  and  19  tons  in  the  St.  Louis  bridge),  or 
100  tons  for  this  limestone  column.  This  same  load  of 
200  tons  would  be  carried  by  a  12"  Z-bar  column  of  4  Z's 
3"  X  6"  X  f",  and  1  plate  8"  X  f"  =  42  sq.  in.  area,  at 
10,000  lbs.  per  sq.  in.  The  economy  of  space  in  this  latter 
column  is  at  once  apparent,  even  disregarding  the  fire- 
proofing  necessary  to  a  limestone  pillar. 

THE  FIRE-PROOFING  OF  COLUMNS. 

As  the  columns  carry  the  greatest  loads  found  in  modern 
buildings  (some  over  1,500,000  lbs.),  the  proper  fire-proof- 
ing of  these  members  becomes  a  most  important  subject  for 
consideration.  In  only  too  many  cases,  however,  is  this 
slighted  even  to  a  very  dangerous  extent,  as  was  proven  by 
the  Athletic  Club  Building  fire,  before  referred  to. 


COL  UMNS. 


133 


The  first  attempts  at  making  fire-proof  columns  were 
through  the  use  of  a  double  column,  one  inside  the  other, 
with  the  intervening  space  filled  with  plaster.  This  idea 
was  patented,  and  reference  may  still  be  found  to  such  con- 
struction in  the  New  York  building  laws,  as :  "  The  said 
column  or  columns  shall  be  either  constructed  double,  that 
is,  an  outer  and  an  inner  column,  the  inner  alone  to  be  of 
sufficient  strength  to  sustain  safely  the  weight  to  be  im- 
posed thereon." 

The  scientific  fire-proofing  of  columns  by  means  of 
terra-cotta  was  started  by  Mr.  P.  B.  Wight  in  1874,  and 
the  Chicago  Club  house,  designed  by  Treat  &  Foltz,  archi- 
tects, was  the  first  instance  where  terra-cotta  gores  were 
used  around  columns.  Many  systems  have  since  been  in- 
troduced, and  both  the  hard  tile  and  the  porous  tile  have 
been  used  extensively.  The  cheapest  method  has  been 
through  the  use  of  shells  ol  hard  terra-cotta  surrounding 
the  column,  but  not  fastened  to  the  metal-work.  This 
system  is  decidedly  faulty  in  placing  so  much  reliance  in 
the  joints  alone  for  stability,  as  the  blocks  are  simply 
hooked  to  one  another,  and  not  to  the  metal  column. 

The  requirements  in  the  adequate  fire-proofing  of  col- 
umns are : 

1.  The  material  must  be  indestructible  by  fire. 

2.  The  material  must  be  non-heat-conducting. 

3.  The  material  must  be  so  secured  to  the  column  that 
it  cannot  be  dislodged. 

The  use  of  hard  fire-clay  tiles  is  only  to  be  recommended 
when  such  tiles  are  hollow,  with  a  proper  air-space  around 
the  metal  column,  and  even  then  experience  seems  to  show 
that  the  hard  tile  is  in  no  way  as  satisfactory  under  great 
heat  as  the  more  porous  kinds.  Applications  of  cold  water 
in  combination  with  heat  have  also  proved  the  hard  tile 
far  less  reliable  in  case  of  conflagration  than  the  porous 


134 


ARCHITECTURAL  ENGINEERING. 


tile.  The  hard  tile  is  very  apt  to  crack  off  under  such 
conditions,  as  has  been  stated  in  the  chapter  on  Floors. 

The  use  of  solid  blocks  of  porous  tile,  well  bedded 
against  the  metal  column,  seems  to  be  the  one  most  highly 
recommended.  Here,  as  in  terra-cotta  floor  arches,  the 
competition  in  price,  which  places  the  better  article  or 
method  at  a  disadvantage,  is  to  be  deplored.  Loosely 
drawn  specifications  are  also  responsible  in  a  great  measure 
for  many  very  common  defects.  All  wiring  of  the  indi- 
vidual blocks  either  to  the  columns  or  to  one  another 


•Hi 

*4 

Fig  80. 


Fig.  82. 


should  be  made  by  means  of  copper  wire.  Figs*  80,  8j,  and 
82  show  the  ordinary  methods  of  placing  the  fire-proof 
furring  for  columns. 

The  Z-bar  columns  in  the  newer  portion  of  the  Monad- 
nock  Building  were  fire-proofed  as  shown  in  Fig.  83  up  to 

E"FDf?DU5T/LE 


/iULLUW  dft/nKs 

Fig.  83. 

and  including  the  eighth  floor.  Hollow  bricks,  laid  in 
cement  mortar,  were  built  solidly  around  the  columns  to  a 


COL  UMNS. 


135 


line  distant  4  in.  from  the  extreme  points  of  the  metal-work, 
and  a  2-in.  coating  of  hollow  tile  was  then  laid  against  the 
brick  backing  extending  beyond  the  column  in  one  direc- 
tion, to  serve  as  a  space  for  vertical  pipes.  The  columns 
above  the  eighth  floor  received  the  hollow-tile  protection 
only. 

The  requirements  for  fire-proofing  the  interior  columns 
of  office  buildings  are  thus  defined  by  the  Chicago  ordi- 
nance : 

"  The  coverings  for  columns  shall  be,  if  of  brick,  not  less 
than  8  inches  thick;  if  of  hollow  tile,  one  covering  at  least 
2 \  inches  thick.  If  the  fire-proof  covering  is  made  of 
porous  terra-cotta,  it  shall  be  at  least  2  inches  thick. 
Whether  hollow  tile  or  porous  terra-cotta  is  used,  the 
courses  shall  be  so  anchored  and  bonded  together  as  to 
form  an  independent  and  stable  structure." 

"  In  all  cases  there  shall  be  on  the  outside  of  the  tiles  a 
covering  of  plastering  with  Portland  cement  or  of  other 
mortar  of  equal  hardness  and  efficiency  when  set." 

"  If  plastering  on  metallic  laths  be  used  as  fire-proofing 
for  columns,  it  shall  be  in  two  layers,  of  which  the  first 
shall  be  applied  in  such  manner  that  the  mortar  will  cover 
the  entire  external  surface  of  the  column,  while  the  space 
between  the  two  layers  shall  be  not  less  than  1  in.  thick." 

"  The  metallic  lath  shall  in  each  case  be  fastened  to 
metallic  furrings,  and  the  plastering  upon  the  same  shall  be 
made  with  cement.  Protection  for  the  lower  five  feet  shall 
be  required  in  this  case  the  same  as  where  porous  terra- 
cotta or  hollow-tile  covering  is  used." 


CHAPTER  VIII. 


WIND  BRACING. 

A  careful  comparison  of  the  treatments  of  wind  forces 
as  applied  to  the  mercantile  buildings  of  to-day,  leads  one 
to  the  conclusion  that  the  designers  differ  very  materially 
in  regard  to  the  forces  to  be  resisted,  the  strength  of  the 
materials  employed,  and  the  most  efficient  details  of  con- 
struction. Indeed,  there  are  buildings  from  ten  to  sixteen 
stories  high  in  the  city  of  Chicago,  that  possess  absolutely 
no  metallic  sway-bracing,  and  others,  scarcely  better,  where 
sway-rods,  as  wind-laterals,  were  attached  to  pins  through 
lugs  on  the  cast  columns,  which  lugs  were  of  an  ultimate 
strength  of,  perhaps,  25  per  cent  of  the  rods.  H.  H. 
Quimby,  in  his  paper  on  "  Wind  Bracing  in  High  Build- 
ings,"* mentions  the  case  of  an  office  building  recently 
erected,  of  seventeen  stories,  or  200  ft.  in  height,  and  60  ft. 
wide  ;  13-in.  walls  were  used  front  and  back,  broken  by  win- 
dows and  bay  windows,  with  wind  bracing  consisting  solely 
of  the  interior  partitions  of  8-in.  box  tile,  with  four  ribs  of 
T9g-  in.  each,  or  2\  in.  thickness  of  tile  in  each  partition.  This 
building  towers  above  its  neighbors  of  five  or  six  stories 
only,  while  but  a  few  blocks  away  is  one  of  seventeen 
stories,  also,  but  150  ft.  wide,  or  2 J  times  the  width  of  the 
former,  with  sway-bracing  consisting  of  15-in.  channel-struts 
and  6-in.  eye-bars.    Such  is  the  diversity  of  practice. 

Some  architects  depend  solely  upon  the  partitions  of 
hollow  tiles  for  the  lateral  stability  of  their  buildings, 

*  Trans.  A.  S.  C.  E.,  Vol.  XXVII,  No.  3. 

136 


WIND  BRACING.  137 

weak  as  the  partitions  must  be  through  the  introduction  of 
numerous  doors  and  office  lights.  This  method  of  filling 
in  the  rectangles  of  the  frame  by  light  partitions  may  be 
efficient  wind  bracing,  but  the  best  practice  would  cer- 
tainly indicate  that  it  cannot  be  relied  upon,  or  even 
vaguely  estimated. 

A  building  with  a  well-constructed  iron  frame  should  be 
safe  if  provided  with  brick  partitions,  and  if  the  base  is  a 
large  proportion  of,  or  equal  to  the  height,  or  if  the  exterior 
of  the  iron  framework  is  covered  with  well-built  masonry 
walls  of  sufficient  thickness ;  for  the  rigidity  of  solid  walls 
would  exceed  that  of  a  braced  frame  to  such  an  extent  that, 
were  the  building  to  sway  sufficiently  to  bring  the  bracing- 
rods  into  play,  the  walls  would  be  damaged  before  the  rods 
could  be  brought  into  action. 

Hence  the  stability  must  depend  entirely  either  on  the 
masonry  or  on  the  iron  framing ;  and  in  veneer  buildings, 
which  are  being  considered  here  in  particular,  the  latter 
system  of  bracing  the  metal-work  must  be  used,  with  the 
walls  as  light  as  possible,  simply  enclosing  the  building 
against  climatic  and  injurious  forces.  This  practice  has 
been  adopted  quite  uniformly  by  the  best  Chicago  archi- 
tects and  engineers,  and  will  alone  be  considered  here  as  a 
method  of  wind  bracing. 

Each  building  offers  its  own  peculiar  conditions  to  the 
carrying  out  of  proper  wind  bracing,  and  many  factors 
must  be  considered  for  a  judicious  solution.  The  height, 
width,  shape,  and  exposure  of  the  structure,  as  well  as  the 
character  of  the  enclosing  walls,  will  determine  the  amount 
of  the  wind  pressure  to  be  cared  for,  while  the  details  of 
construction,  the  internal  appearance,  and  the  planning  of 
the  various  floors  will  largely  influence  the  manner  in 
which  this  bracing  is  to  be  treated.  The  architectural 
planning  of  the  offices,  rooms,  and  corridors,  often  raises 


138 


ARCHITECTURAL  ENGINEERING. 


most  serious  obstacles  to  a  proper  arrangement  of  wind 
bracing,  and  the  engineer  is  frequently  called  upon  to 
make  most  generous  concessions  in  favor  of  doors,  win- 
dows, passages,  and  even  whole  areas,  as  is  sometimes 
demanded  in  banking-  or  assembly-rooms  and  the  like. 
Such  considerations  have  led  to  the  development  of  the 
portal  type  of  wind  bracing.  As  more  and  more  of  the 
constructional  work  of  large  buildings  is  placed  in  the  care 
of  the  engineer,  as  opposed  to  the  purely  architectural  or 
decorative  draughtsman,  just  so  will  the  former  insist  that 
a  proper  regard  for  construction  is  of  equal  value  with  the 
artistic  portion  of  the  work.  The  one  must  supplement 
the  other,  instead  of  giving  way  to  irrationalities  of  design. 

Two  distinct  corps  of  workmen  are  found  in  the  offices 
of  the  more  prominent  architects  of  the  day  :  the  archi- 
tectural draughtsmen,  for  all  decorative  design  and 
work,  and  the  engineers,  who  have  charge  of  the  con- 
structional problems,  as  indicated  in  this  outline.  In  such 
an  office  the  two  kinds  of  work  can  be  carried  on  simul- 
taneously, concessions  made  on  both  sides,  and  a  satisfac- 
tory medium  reached. 

Quimby,in  his  article  on  wind  bracing,  favors  the  pro- 
vision of  a  4o4b.  wind  pressure,  with  iron  or  steel  bracing 
strained  not  over  \  of  the  ultimate  strength  ;  while  George 
A.  Just,  in  a  discussion,  advocates  the  use  of  30  lbs.  Cir- 
cumstances must  to  a  great  extent  govern  the  choice  of 
the  designer.  The  shape  and  exposure  of  the  structure, 
and  the  solidity  of  the  enveloping  walls,  will,  as  said  above, 
largely  determine  the  amount  of  wind  pressure  to  be  car- 
ried by  the  metallic  bracing ;  but  if  such  bracing  be  relied 
upon  entirely,  a  unit  of  30  lbs.  should  serve  as  a  minimum. 
The  following  was  adopted  by  E.  C.  Shankland,  Chief  En- 
gineer of  the  World's  Columbian  Exposition :  For  roof 
trusses,  40  lbs.  per  horizontal  sq.  ft.  of  roof  taken  vertical, 


WIND  BRACING.  139 

or  25  lbs.  per  sq.  ft.  taken  vertical  in  addition  to  the  effect 
of  30  lbs.  wind  acting  under  an  angle  of  200  with  the 
horizon,  whichever  will  give  the  largest  result.  On  pur- 
lins and  jack  rafters  take  30  lbs.  per  horizontal  sq.  ft.;  on 
gallery  floors  take  80  lbs.  per  horizontal  sq.  ft.;  on  main 
floors  take  100  lbs  per  horizontal  sq.  ft.  A  horizontal  wind 
pressure  of  30  lbs.  per  sq.  ft.  shall  be  taken  care  of  unless 
otherwise  decided  by  the  Engineer  of  Construction.  All 
details  must  be  carefully  calculated  both  for  bearing  and 
shear. 

Many  and  many  are  the  architects  who  have  used  cast- 
iron  columns  piled  story  on  story,  with  tile  partitions  only 
as  a  wind-resisting  medium,  and  their  structures  stand,  to 
become  a  source  of  wonder  to  the  engineering  profession. 
But  in  a  field  of  such  great  uncertainty  any  judicious  in- 
crease in  safety  is  in  the  nature  of  insurance,  and  must  not 
be  regarded  as  wasted,  simply  because  never  destroyed. 

Wind  bracing  must  reach  to  some  solid  connection  at 
the  ground.  It  should  also  be  arranged  in  some  symmet- 
rical relation  to  the  building  outlines.  If  the  building 
is  narrow  and  braced  crosswise  with  one  system,  the  brac- 
ing should  be  midway,  while  if  two  systems  are  employed, 

3 

Fig.  84.  Fig.  85.  Fig.  80.  Fig.  87. 

(1)  (2)  (3)  (4) 

they  should  be  placed  equidistant  from  the  ends.  This 
symmetry  is  necessary  to  secure  the  equal  services  of  both 
systems,  thus  preventing  any  twisting  tendencies. 


ft'  1 

V 

h 

r 

A 

f  > 

140 


ARCHITECTURAL  ENGINEERING. 


The  more  common  forms  in  ordinary  practice  are  shown 
in  Figs.  84,  85,  86,  and  87. 

Each  type  must  be  hgured  properly,  as  the  strains  in 
the  horizontal  members  and  the  columns  are  essentially 
concerned  in  the  calculations.  The  problem  is  not  capable 
of  exact  solution,  owing  to  several  indeterminable  factors 
that  enter  into  the  computations,  and  the  consequent  equal 
number  of  assumptions  that  must  be  made.  The  stresses 
in  the  wind  bracing  will  be  maximum  when  the  direction  of 
the  wind  is  normal  to  the  exterior  wall,  or  parallel  to  the 
plane  of  bracing.  This  condition  is,  therefore,  assumed. 
A  further  assumption  is  made  that  the  floors  are  suffi- 
ciently rigid  to  transmit  the  horizontal  shears  due  to 
wind. 

The  external  forces  will  be  the  same  whichever  of  the 
four  methods,  shown  in  the  figures  above,  is  used,  provided 
the  exposed  areas,  panels,  etc.,  are  the  same.  The  hori- 
zontal external  force  at  any  panel  point  will  be  equal  to  the 
distance  between  the  systems  (at  right  angles  to  the  brac- 
ing) times  the  distance  between  floors  half-way  above  and 
half-way  below,  times  the  assumed  wind  pressure  per  sq. 
ft.  The  total  shear  at  any  point  equals  2  forces  at  or 
above  the  point  taken. 

These  shears  are  undoubtedly  reduced  to  some  con- 
siderable extent  through  many  practical  considerations. 
The  dead  weight  of  the  structure  itself,  the  resistance 
to  lateral  strains  offered  in  the  stiff  riveted  connections 
between  the  floor  systems  and  the  columns,  the  stiffen- 
ing effects  of  partitions  (if  continuously  and  strongly  built), 
and  linings,  coverings,  etc.,  all  tend  to  decrease  the  distort- 
ing effects  of  the  wind  pressure.  But,  in  view  of  the  un- 
certainty in  regard  to  the  efficiency  of  these  latter  con- 
siderations, they  may  not  be  relied  upon,  and  are  therefore 
disregarded  in  the  calculations. 


WIND  BRACING. 


[41 


SWAY-RODS  (i). 

The  simplest  case  of  wind  bracing  is  shown  in  Fig. 
84.  Considering  one  bay  alone  as  braced,  the  system  may 
be  analyzed  as  follows :  Referring  to  the  upper  story 
of  a  framework,  as  shown  in  Fig.  88,  Px  =  pHlLx  where 
Px  =  resultant  wind  pressure  on  upper  story,/  =  unit-press- 
ure, and  Hx  and  Z,  equal  respectively  the  height  and  width 
of  the  area  affecting  the  bracing  in  the  panel  under  con- 
P 

sideration.  — 1  must  then  be  the  horizontal  component  of 


Hoof.. 


Fig.  88. 

the  stress  in  the  diagonal,  and  the  tension  in  this  diagonal, 
making  an  angle  0  with  the  horizontal,  must  be 


T  =  —  sec  ft 
2 

The  diagonal  tension  in  the  second  story  from  the  top  will 
be  T%  —       +  Pj  sec  0,  where  P  =  wind  pressure  on  any 

single  story,  assuming  them  to  be  of  equal  height.  ~  -f-  P  — 
compressive  stress  in  the  horizontal  strut  at  the  top-floor 
level.    In  like  manner,  7",  =       -f-  2      sec  ft 

The  tension  in  the  diagonal  rods  will  cause  a  decrease 


142  ARCHITECTURAL  ENGINEERING. 

in  loads  on  the  windward  columns,  and  an  equal  increase 
in  loads  on  the  leeward  columns.  Calling  this  increase  or 
decrease  Vv  we  have 

V.  =  —j-,  where  hx  —  — . 
1       /  '  1  2 

In  a  similar  manner, 

Ph  Ph 

V3  must  equal  V9  -f-  the  vertical  component  of  the  diagonal 

Ph 

7*3,  or  V3  —  — j1  +      sm        This  will  serve  as  a  check 

on  the  calculations. 

These  wind  loads  Vv  V2  etc.,  must  be  added  to  all  the 
other  regular  loads  on  the  columns.  In  the  columns  I,  3, 
etc.,  the  direct  or  dead  loads  carried  by  the  columns  resist 
the  upward  vertical  components  of  the  stresses  in  the  rods 
connected  to  the  bottoms  of  these  columns.  Thus  the 
dead  load  in  column  3  is  reduced  by  the  full  amount  of  the 
upward  compressive  strain  from  wind  in  that  column,  or 
F2,  and  if  this  amount  were  to  equal  or  exceed  the  dead 
load  in  column  3,  tension  would  occur  in  the  connection  of 
this  column  to  the  one  below. 

It  will  be  seen  that  the  increment  to  the  stress  V  at 
each  floor  may  be  eccentric,  as  shown  in  Fig.  95,  the 
length  of  the  arm  equalling  the  distance  from  the  point  of 
attachment  to  the  horizontal  strut,  to  the  centre  of  the 
column  itself.  If  this  connection  were  at  the  axis  of  the 
column,  the  eccentricity  would  be  reduced  to  o,  and  the 
eccentric  load  become  a  dead  load. 

Take  the  case  of  a  typical  skeleton  building,  fourteen 
stories  in  height,  of  12  feet  each,  24  foot  front,  and 
columns  spaced,  12  feet  apart  in  the  depth  of  the  build- 
ing. Assuming  that  stiffness  against  side-yielding  alone  is 
necessary,  place  diagonal  members  in  each  story,  as  in 
Fig.  89,  utilizing   the   floor-girders   as   struts,   with  the 


WIND  BRACING. 


143 


columns  as  chords.  At  30  lbs.  per  square  foot  wind  press- 
ure the  panel  load  equals  4,300  lbs.  Con- 
sidering the  protection  afforded  by  neigh- 
boring buildings,  the  point  of  application 
of  the  resultant  wind  pressure  will  be 
taken  at  two  thirds  of  the  height  of  the 
structure  above  ground.  The  total  shear 
will  then  equal  about  60,000  lbs.,  or  30 
tons.  In  the  basement  panel,  then,  sec  6  = 
1. 1 2,  giving  33.6  tons  tension  in  the  cellar 
diagonal.  The  moment  of  the  resultant 
wind  pressure  =  30  X  118  =  3,540  foot-tons, 
and  this,  divided  by  24,  gives  147^-  tons  ten- 
sion at  the  windward  foundation.  The 
vertical  component  of  the  basement  di- 
agonal =  16.8  tons,  leaving  a  compression 
of  about  131  tons  on  the  leeward  column. 

The  dead  weight,  including  iron,  walls, 
floors,  filling,  etc.,  will  equal  about  250 
tons  for  one  foundation,  while  even  for  a 
building  with  no  filling  or  partitions  com- 
pleted, the  dead  weight  is  still  some  200  tons,  thus  render- 
ing anchorage  unnecessary. 

If,  in  the  same  cross-section  of  the  building,  n  bays  not 

adjacent  are  braced  by  means  of  diagonal  rods,  the  tension 

P  Ph 
T  becomes  T.  —  — 1  sec  6,  and  V,  =  — V. 

The  bracing  in  Fig.  85  may  easily  be  analyzed  in  a 
manner  similar  to  the  above. 

The  highest  building  in  the  city  of  Chicago  is  the 
Masonic  Temple,  273'  10"  from  grade  to  top  of  coping.  A 
cross-section  of  this  building  is  shown  in  Fig.  90,  with  one 
system  of  bracing-rods.  It  will  be  seen  that  a  combination 
of  forms  (1)  and  (2)  was  used,  the  bracing  being  arranged  to 


i44 


ARCHITECTURAL  ENGINEERING. 


suit  halls  and  doorways.  In  this  building  the  sway-rods 
were  not  connected  to  the  floor-beams  themselves,  but  to 
special  I  beams  placed  between  the  columns  and  just  below 
the  floor  system. 

In  "  The  Fair"  Building,  system  i  was  used,  but  with 
lattice  girders  from  column  to  column,  serving  as  struts 
and  floor-beams  at  the  same  time.  Gusset-plates  were 
dropped  below  the  girder  to  receive  the  pins  for  connec- 
tion with  the  turnbuckle  rods. 

One  of  the  best  examples  of  system  (i)  of  wind  bracing 

in  Chicago,  the  writer  found 
to  be  that  described  by  Mr. 
C.  T.  Purdy  in  his  article 
in  the  Engineering  News  of 


Fig.  90. 


Fig.  91. 


December,  1891.  This  building,  the  Venetian,  is  of  the 
veneer  type,  and  contains  some  excellent  details.  The 
floor  plan  is  shown  in  the  accompanying  figure  (91)  with  the 


WIND  BRACING.  1 45 

four  sets  of  sway-rods  given.  Each  set  of  bracing  is  there- 
fore figured  to  resist  a  wind  pressure  for 
an  area,  the  horizontal  width  of  which 
is  equal  to  one  fifth  the  depth  of  the 
building,  and  the  height  of  which  is  the 
height  of  the  building.  The  area  tribu- 
tary to  each  floor  X  40  lbs.  equals  the 
horizontal  shear  at  each  floor  or  panel- 
point,  while  the  total  shear  at  any  floor 
equals  the  sum  of  the  shears  acting  on 
the  panel-points  directly  above,  as  we 
have  seen  before.  It  was  not  considered 
necessary,  however,  to  carry  the  whole 
amount  of  this  shear  into  the  steel  brac- 
ing. The  practical  considerations  which 
tend  to  diminish  the  distorting  effect  due 
to  a  lateral  force,  decided  that  but  70  per 
cent  of  these  shears  needed  to  be  cared 
for  by  the  bracing,  leaving  30  per  cent 
to  be  taken  up  by  the  other  factors. 
The  strains  and  sections  for  one  bay  are 
here  given  (Fig.  92). 

All  the  columns  affected  by  this  brac- 
ing were  made  continuous  from  the  foundations  to  the 
second-floor  level,  and  portals  were  used  to  take  the  place 
of  the  diagonal  rods  in  two  instances  where  rods  were  out 
of  the  question.  This  occurred  on  a  main  floor  devoted  to 
large  banking-rooms.  The  bending  moments  due  to  these 
portals  were  taken  up  in  the  columns.  In  the  case  where 
the  rods  came  down  to  the  first-floor  level,  the  bottom 
strut  was  connected  to  the  columns  so  as  to  take  both  ten- 
sion and  compression  horizontally,  as  well  as  to  resist  the 
component  of  the  rod  strains.  This  insured  the  resistance 
of  both  columns  to   the   horizontal   thrust  of  the  strut, 


146 


A  R  CHI  TE  CT  URA  L  ENGINEERING. 


whichever  pair  of  rods  was  strained,  and  the  columns  were 
calculated  to  resist  the  bending  moment  incurred,  as  well 
as  to  carry  the  regular  column  loads. 

With  the  use  of  the  portals,  the  columns  were  designed 


*4 


1 »  I  W Ji/y/v 


2SffC//AA/NELS  J2  2-133.  \ 


Fig.  93. 


to  resist  the  bending  moment  which  the  stopping  of  the 
rods  necessitated,  and  as  a  further  assurance  that  these  con- 
nections should  be  as  strong  as  the  rest  of  the  system,  the 


Fig.  94. 


top  connections  of  all  of  the  first-floor  beams  were  omitted, 
and   the   clearance   spaces   between  all  the   beams  and 


WIND  BRACING.  1 47 

columns  were  driven  tight  with  thin  metal  wedges,  until 
the  girders  and  beams  passing  along  the  column  axes  were 
continuous  and  in  compression  out  to  the  sidewalk  walls, 
which  latter  are  backed  by  the  solid  street. 

The  horizontal  channel-struts  are  shown  in  Fig.  93. 
They  were  used  as  shown  up  to  and  including  the  seventh 
floor.  A  lighter  section  was  used  for  the  floors  above.  A 
slight  connection  only  was  made  between  the  channel- 
struts  and  the  columns.  The  struts  were  planed  at  both 
ends,  with  no  clearance,  thus  making  butt  joints  with  the 
columns.  A  bent  plate  between  the  channels  provided 
holes  for  four  rivets  connecting  to  the  columns,  but  they 
were  hardly  necessary.  Underneath  the  ends  of  these 
struts  a  cast-iron  block  was  bolted  to  the  column  and  sup- 
ported by  two  bracket-angles  beneath,  with  sufficient  rivets 
to  resist  the  vertical  compression  of  the  rods  in  this  direc- 
tion (see  Fig.  94). 

Above  the  ends  of  the  struts  other  cast-iron  blocks  were 
used,  planed  top  and  bottom,  thus  allowing  them  to  fit  in 
tightly  between  the  tops  of  the  struts 
and  the  cap-plates  of  the  columns. 
These  blocks,  therefore,  fitted  into  the 
recesses  made  by  the  flanges  of  the 
Z-bars  so  closely  that  the  f"  cap- 
plates  were  brought  into  direct  shear 
entirely  around  three  sides  of  the 
blocks.  The  shear  resistance  of  the 
plate,  together  with  the  weight  of  the 
beam  on  it,  was  more  than  sufficient 
to  resist  the  upward  vertical  com- 
ponent of  the  rods.  Such  cast-iron 
blocks  in  this  connection  are  very 
convenient  for  use,  for  it  often  hap- 
pens that  the  bracket-angles  cannot  be  brought  directly 


Fig.  95 


148 


A R CHITECTURA  L  ENGINEERING. 


under  the  channels  of  the  struts,  and  the  medium  between 
the  strut  and  the  bracket-angles  must  act  as  a  beam  as 
well  as  a  filler.  Fig.  95  shows  a  partial  cross-section  of 
the  building  with  doorway,  etc.  This  shows  the  reason  for 
placing  the  pin-points  so  far  from  the  column  centres. 
The  channel-struts  are  reinforced  with  cover-channels  to 
resist  the  bending  moment  on  the  strut  caused  by  thus 
moving  the  pin-centres. 

The  diagonal  rods  in  this  building  were  proportioned  on 
a  basis  of  20,000  lbs.  per  sq.  in.  All  rods  had  turnbuckles, 
and  no  rods  were  of  an  area  less  than  square.  The 
Ashland  Block,  by  Burnham  &  Root,  Chicago,  has  longer 
struts  than  those  in  the  Venetian  Building,  15"  channels 
being  used  in  the  floors,  acting  both  as  struts  and  floor- 
beams. 

PORTAL  BRACING  (3). 

The  third  method  of  wind  bracing,  called  the  portal 
system,  may  be  analyzed  as  follows  (see  Fig.  96) :  Taking 
the  upper  floor  first,  the  external  force  P1  may  be  considered 
as  producing  equal  horizontal  reactions  at  the  bottoms  of 

P 

the  portal  legs,  or  at  the  floor  level,  equal  to  — 1  each.  A 
wind  moment  M  is  also  produced  at  this  floor  level,  or, 

M  —  Pxhx ,  where  h,  —  —. 

Owing  to  the  rigidity  of  the  framework,  this  wind 
moment  will  be  resisted  by  the  resisting  moment  of  the 
column  sections,  and  by  the  portal  connections  at  the  floor- 
line.  This  resisting  moment  must  equal  - where  f  =  the 
unit-strain  on  extreme  fibres,/,  =  distance  of  extreme  fibres 


WIND  BRACING. 


149 


from  the  neutral  axis,  and  /  =  moment  of  inertia  of  the 

section.    But  M  =  Pxhx  hence  /  =  ^-^A 

/  will  be  slightly  different  on  the  two  sides  of  the  neutral 
axis.   On  the  compression  side  of  the  bay,  /  will  be  taken  as 


the  moment  of  inertia  of  the  section  of  the  column  and  the 
portal,  while  on  the  tension  side,  /  must  be  taken  for  a  sec- 
tion of  the  column  and  the  bolts  securing  the  portal  to  the 
floor-beam  or  to  the  portal  below.  If  a  splice  occurs  in  the 
column  on  the  tension  side,  /  must  be  taken  for  the  sections 
of  the  bolts  connecting  the  cap-plates  of  the  column,  and 
for  the  bolts  through  the  portal  and  floor-beam. 

The  decrease  of  load  on  the  one  column,  and  the  equal 
increase  in  load  on  the  other  column  will  be  as  before,  or 


Fig.  96. 


150 


ARCHITECTURAL  ENGINEERING. 


P  k 

Vx  =  -j1-    In  column  2,  the  vertical  column  load  Vx  due  to 

wind,  must  be  added  to  the  regular  column  load,  the  same 
as  in  previous  discussion.  Vx  must  also  equal  the  shear  on 
all  vertical  planes. 

The   horizontal   shear  along  the  line  aa  =  Px,  while 
the  horizontal  shear  in  either  leg  or  portal  or  at  bottom 
P 

of  leg  =  — .     These  shears  will  determine  the  thickness  of 
°  2 

the  webs.  The  connections  of  the  portal  to  the  column  on 
either  side  must  equal  the  total  vertical  shear. 

Taking  moments  about  the  line  dd,  it  will  be  found  that 
=  O.  That  is,  there  is  no  bending  moment  along  the 
line  dd,  and  neither  the  floor-beams  nor  portals  are  strained 
by  bending  moment  along  this  line. 

For  a  maximum  stress  in  the  flange  C  take  a  point  in 
flange  A,  distant  x  from  line  dd,  and  distant  y,  at  right 
angles,  from  flange  C.  Then  x  times  the  vertical  shear 
divided  by  y  —  stress  at  section  taken,  and  this  is  maximum 
x 

when  -  has  its  maximum  value.    The  stress  in  the  flange  A 

may  be  obtained  in  a  similar  manner. 

The  leg  of  the  portal,  including  column  2,  may  also  be 

P 

taken  as  a  cantilever,  with  the  two  forces  —  and  V.  acting: 

2  i  s 

on  it.    The  flange  C  will  be  in  compression,  the  column 

itself  acting  as  a  tension  chord.    Assume  a  point  on  the 

centre  line  of  the  column,  distant  xx  from  bottom  of  leg, 

and  at  distance^  from  the  flange  C,  at  right  angles.  Then 

P  x  .  x 

— -—  =  strain  in  flange  C,  and  this  is  maximum  when  —  is 

maximum.  There  is  a  slight  error  in  this  treatment,  but  it 
is  on  the  side  of  safety.  If  the  flange  C  is  proportioned  for 
these  maximum  stresses,  the  requirements  will  be  fulfilled. 


WIND  BRACING. 


5' 


PA 


In  the  second  story  from  the  top,  V%  =  considering 

Pa  =  2P1S  or  that  the  stories  are  of  equal  height.  The  con- 
centric load  Vx  in  column  2  from  the  column  above,  and  its 
equal  reaction,  may  be  omitted  in   a  calculation  of  the 


'  2*7g"  f  


wet  ffdm/rp/f/ftA 
— f—  w 


2  T  /a  V/?  T  &  v  1 

FlG.  97. — Portal-strut  used  in  the  Monadnock  Building. 


strength  of  the  portal  bracing  (as  they  are  applied  along  the 
same  straight  line),  as  may  also  the  equal  negative  effects  in 
column  1. 

The  vertical  shear  in  this  second-story  bracing  will 


SKYltfHT 

5PAC£  % 

in 

Amnom 

ni 

in 

/6r"nooff 

ni 

in 

/5T"fL00/f 

ni 

in 

nl 

Fig.  98. 

equal  S2  =  V2  —  Vx.    The  horizontal  shear  across  the  top 

P 

of  the  portal  =  P2,  while  in  either  leg  the  shear  = 


One  of  the  first  attempts  at  a  portal  system  in  building 


152 


ARCHITECTURAL  ENGINEERING. 


construction  was  through  the  use  of  a  portal-strut  used  in 
the  older  portion  of  the  Monadnock  Building,  as  in  Fig.  97. 

The  portal  system  (3)  was  used  in  the  Old  Colony 
Building,  Chicago,  completed  in  1894.  The  portals  are 
placed  at  two  planes  in  the  building — a  cross-section  of  one 
set  being  shown  in  Fig.  98.  Wind  pressure  was  figured  at 
27  lbs.  per  square  foot  on  one  side  of  the  building  at  a 
time.  Each  portal  was  calculated  independently  for  the 
sections  of  both  top  and  bottom  flanges,  thickness  of  web, 
cross-shear  on  rivets  connecting  the  curved  flanges,  and  for 


Fig.  99. — Detail  of  Portal,  Old  Colony  Building. 


all  splices  and  connections.  A  detail  of  one  portal  is  shown 
in  Fig.  99.  This  arrangement  of  wind  bracing  proved  very 
satisfactory  in  all  respects,  and,  according  to  the  designer, 
was  cheaper  in  the  end  than  the  sway-rods  provided  in  the 


WIND  BRACING. 


153 


first  design;  but  the  writer  would  question  whether  portal 
bracing  can  be  provided  cheaper  than  tension-rods,  as 
claimed.  With  good  details  in  connections  and  proper 
regard  for  their  location  in  the  original  planning  of  the 
building,  sway-rods  can  be  used  without  great  expense  or 
trouble.  The  portal  arrangement  certainly  makes  a  fine 
interior  appearance  if  the  arched  openings  are  given  a 
slight  decorative  treatment  in  plaster,  as  was  done  in  the 
Old  Colony  Building.  The  floor  plan  will  generally  govern 
the  use  of  either  one  or  the  other  system,  whether  the 
rooms  are  to  be  connected  by  large  openings  or  small 
doorways. 

KNEE-BRACES  (4). 

The  system  of  knee-braces,  or  arrangement  (4)  for 
wind  bracing,  is  not  an  economical  method,  as  it  produces 


Fig.  100. 


heavy  bending  moments  in  both  the  horizontal  struts  and 
in  the  columns  themselves.  This  system  may  be  analyzed 
as  follows  (see  Fig.  100) 


154 


ARCHITECTURAL  ENGINEERING. 


The  shear  at  the  top-floor  level  will  be  ~  at  each  column. 

P  h 

Then  as  before,  Vt  —  -y-1. 

The  tension  in  the  brace  cb  is  nearly 
Pt  i  P,H, 

There  will  be  an  equal  amount  of  compression  in  the  oppo- 
site brace.  This  suggests  the  use  of  knee-braces  capable 
of  resisting  both  compression  and  tension.  There  will 
be  a  bending  moment  at  C  whose  value  is  approximately 

P    h       Ph  h 
M=  -l  .  —  =  —  --.    The  factor  —  is  used,  as  the  column 
224  2  ' 

is  considered  as  square-ended  and  fixed  by  the  static  load 


 ^ 


Fig.  ioi. — Knee-bracing  used  in  the  Isabella  Building. 

and  by  bolts.    This  bending  moment  will  also  exist  at  d. 

Phi 

At  b  there  will  be  a  bending  moment  My  —  VJ2  =  1  £  2. 
This  type  of  wind  bracing  was  used  in  the  Isabella 


WIND  BRACING. 


155 


Building-,  by  W.  L.  B.  Jenney,  architect,  as  shown  in 
Fig.  10 1. 

A  modification  of  the  knee-brace  system  of  wind  brac- 
ing was  employed  in  the  new  Fort  Dearborn  Building 
(1894-95,)  by  Jenney  &  Mundie,  architects,  Chicago.  In  this 
case  a  wind  load  of  40  lbs.  per  sq.  ft.  was  taken,  and  the 
assumption  made  that  25  per  cent  of  this  wind  load  would 
be  resisted  by  the  rigid  connections  provided  between  the 
columns  and  the  floor  system,  leaving  75  per  cent,  or  30  lbs. 
per.  sq.  ft.,  to  be  taken  up  by  the  exterior  columns.  This 
was  done  by  using  channel  girders  between  the  columns  in 


I©  ©  ©"©"©"© 


•  ©  ©  0  G 

•  © 

•  © 

•  © 

1  ©  1 

Fig,  102. — Gusset-plate  Bracing  used  in  Fort  Dearborn  Building. 

the  exterior  walls,  with  gusset-plate  connections  to  the 
columns,  as  shown  in  Fig.  102,  10  in.  and  12  in.  channels 
being  used  generally.  In  the  lower  stories,  where  the 
wind  moment  necessitated  it,  a  double  system  of  gusset 
connections  was  used,  under  and  above  the  channel  girders, 


i56 


ARCHITECTURAL  ENGINEERING. 


A  somewhat  similar  method  was  used  in  a  building  in 
New  York  City,  120  ft.  in  height  and  24  ft.  frontage, 
designed  by  L.  de  C.  Berg.  The  Z  columns  were  used, 
spaced  12-ft.  centres,  and  anchored  to  foundations.  At 
three  levels  in  the  building  occur  riveted  girders  in  the 
exterior  walls ;  the  girders  connect  to  the  columns  by 
large  gusset-plates.  At  these  levels,  diagonal  ties  of  flats 
are  also  run  horizontally  over  the  floor  system.  An  addi- 
tional load  of  15  lbs.  vertically  was  figured  in  the  columns 
and  girders  for  the  effect  of  the  wind.  A  similar  system 
of  horizontal  flats  was  also  used  in  the  old  Monadnock 
Building,  Chicago.  In  the  Reliance  Building  the  wind 
strains  were  transferred  from  story  to  story  on  the  table-leg 
principle.  24-in.  plate  girders  were  used  in  the  exterior 
walls  at  each  floor  level,  as  in  Fig.  73. 

The  effects  of  earthquakes  would  scarcely  seem  to  war- 
rant much  consideration  in  our  latitude,  though  Quimby 
and  those  who  discuss  his  article,  give  considerable  promi- 
nence to  it.  "  The  only  safeguard  against  an  earthquake  is 
a  system  of  bracing  with  some  elastic  material  of  positive 
strength,  that  will  so  unify  a  structure  that  it  will  hold 
together,  even  to  the  point  of  overturning  bodily." 

The  Chicago  skeleton  construction  has  been  adopted  in 
San  Francisco,  where  the  fear  of  earthquakes  has,  hereto- 
fore, been  sufficient  to  keep  investors  from  erecting  high 
buildings.  The  new  Chronicle  building  and  the  Croker 
and  Mills  buildings  are  of  the  Chicago  type,  twelve  stories 
and  over  in  height,  and  nave  served  as  precedents  in 
that  locality. 

From  a  consideration  of  the  wind  strains  in  a  building 
it  would  seem  that  a  seventh  point  should  be  added  to  the 
list  of  headings  under  the  discussion  of  columns,  namely  : 

7.  Column  Joints.  — "  The  stability  of  the  individual 
columns  in  a  framed  structure  is  an  element  of  resistance  of 


WIND  BRACING.  I  5/ 

considerable  value  if  the  connections  are  rigid,"  and 
"  wherever  adequate  rod-bracing  is  not  provided,  join  the 
columns  by  complete  splices,  making  them  continuous,  each 
column  a  unit,  to  fail  only  by  breaking  or  bending." 

Although  Quimby  seems  to  limit  the  necessity  of  such 
continuity  to  cases  in  which  no  wind  bracing  is  provided, 
the  writer  believes  that  the  method  of  column  joints  at 
each  and  every  floor  level  is  wrong,  whether  wind  bracing 
be  provided  or  not,  and  that  the  tendency  should  rather 
be  toward  design  with  continuous  columns,  and  riveted 
members  for  the  main  girders  and  spandrel  sections  in  the 
walls.  Nor  should  efficient  wind  bracing  be  neglected 
even  with  these  additional  factors. 

Columns  have  generally  been  of  single  floor  lengths, 
with  I"  cap-plates  on  top,  with  the  beams  connected 
to  the  columns  by  rivets  through  both  top  and  bottom 
flanges,  those  through  the  bottom  flange  passing  also 
through  the  bed-plate  and  the  angle  riveted  to  the  column 
beneath  (see  Fig.  78).  Connections  to  the  bed-plate  only 
should  always  be  avoided,  as  the  lateral  strain  to  be  re- 
sisted should  go  to  the  column  and  not  to  the  bed-plate. 
The  columns  are  usually  connected  to  each  other  by  at 
least  four  rivets,  spaced  on  opposite  sides,  as  far  from 
the  centre  of  the  column  as  possible,  and  passing  through 
the  cap-plate  and  connection-angles  of  each  column.  If 
this  is  done,  every  rivet  driven  tends  to  stiffen  the  connec- 
tion of  the  columns.  If  the  girder  loads  are  heavy,  bracket 
angles  must  be  provided  in  the  lower  column  to  take  the 
shear  off  the  cap-plate.  At  least  3f-in.  bearing  in  full  is 
given  to  each  beam,  and  the  columns  should  be  carefully 
planed  on  the  ends,  and  at  true  right  angles  to  the  column 
axes. 

This  method  of  bracketing  the  tiers  of  columns  together 
by  means  of  angles  or  bent  plates,  gives  a  detail  that  is 


158 


ARCHITECTURAL  ENGINEERING. 


sufficient  to  prevent  lateral  displacement,  but  because  of 
the  elasticity  of  the  brackets  in  bending,  and  the  large 
ratio  of  the  height  of  the  column  to  the  base,  contributes 
very  little  to  the  rigidity  of  the  structure.  The  overturn- 
ing or  lift  on  the  windward  side  is  almost  always  less  than 
the  resistance  due  to  dead  weight ;  but  the  shear  is  liable 
to  be  overlooked,  tendings  as  it  does,  to  topple  over  all  of 
the  columns  of  a  story.  The  column  connection  described 
is  not  stiff  enough  to  prevent  a  slight  movement,  which  can 
be  prevented  by  wind  bracing  only  ;  and  even  with  wind 
bracing,  it  introduces  a  weakness  of  the  column  at  the 
floor  level,  which  the  writer  believes  can  be  obviated  by 
continuous  columns. 

In  the  Masonic  Temple,  the  use  of  columns  of  two- 
storied  lengths  was  tried,  as  an  additional  factor  of  stiff- 
ness in  so  high  a  building,  with  the  joints  "  staggered," 


Fig.  103. 


or  each  column  breaking  joints  with  its  neighbor.  The 

next  step  was  to  discard  the  bed-plates  entirely,  using 
vertical  connection-plates  for  all  column  splices.    Fig.  103 


WIND  BRACING.  I  59 

shows  a  column  splice  with  connections  for  the  floor- 
girders  and  wind  bracing,  used  in  the  new  Pabst  Building, 
Milwaukee,  by  S.  S.  Beman,  architect.  The  floor-girders 
are  made  of  latticed  channels,  and  the  sway-rods  are  con- 
nected to  the  vertical  splice-plates  of  the  columns  much  as 
the  laterals  in  bridge-work  are  connected  to  the  chords. 

The  following  clauses  relating  to  the  splicing  of  the 
Gray  columns  used  in  the  Reliance  Building  are  from  the 
specifications  for  the  steelwork:  "The  columns  will  be 
made  in  two-story  lengths,  alternate  columns  being  jointed 
at  each  story. 

"The  column  splice  will  come  above  the  floor,  as  shown 
in  the  drawings.  No  cap-plates  will  be  used.  The  ends  of 
the  columns  will  be  faced  at  right  angles  to  the  longitud- 
inal axis  of  the  column,  and  the  greatest  care  must  be  used 
in  making  this  work  exact. 
The  columns  will  be  con- 
nected, one  to  the  other,  by 
vertical  splice-plates,  sizes  of 
which,  with  number  of  rivets, 
are  shown  on  the  drawings. 
The  holes  for  these  splice- 
plates  in  the  bottom  of  the 
column  shall  be  punched  -§-  in. 
small.  After  the  splice-plates 
are  riveted  to  the  top  of  the 
column,  the  top  column  shall 
be  put  in  place  and  the  holes 
reamed,  using  the  splice-plates 
as  templates.  The  connections  of  joists  or  girders  to 
columns  will  be  standard  wherever  such  joists  or  girders 
are  at  right  angles  to  connecting  faces  of  columns.  Where 
connections  are  oblique,  special  or  typical  details  will  be 
shown  on  the  drawings." 


i6o 


ARCHITECTURAL  ENGINEERING. 


Fig.  104  shows  a  typical  detail  of  a  column  splice  in 
the  Reliance  Building,  where  the  framing  for  a  bay  win- 
dow joins  the  column. 

Foster  Milliken,  in  his  discussion  of  Quimby's  article, 
classifies  the  points  constituting  a  perfect  joint  as  follows : 

1.  Continuity  of  column  from  cellar  to  roof. 

2.  Proper  connections  for  load  and  proper  distribution. 

3.  Facility  of  connections  for  wind  bracing. 

4.  Ready  alignment. 

5.  Simplicity  of  design,  facilitating  erection. 

He  adds  that  the  ideal  column  would  be  one  tapering 
uniformly,  with  the  section  varying  from  floor  to  floor  with 
the  loads,  advocating  the  continuous  Phoenix  column  with 
pintle-plate  connections,  as  before  described.  Any  such 
system  as  this,  demanding  built  sections  of  plates  and  angles 
for  girders,  instead  of  the  conventional  rolled  beams,  would 
certainly  give  much  more  efficient  connections  with  the 
columns;  and  joints  may  be  designed  adding  greatly  to 
the  rigidity  of  the  structure,  even  where  the  regular  trans- 
verse bracing  is  omitted,  or  where  it  interferes  seriously 
with  the  necessary  openings  in  the  partitions. 

For  the  theoretical  limit  in  the  height  of  a  building, 
considering  the  wind  pressure,  we  may  assume  that  the 
wind  acts  against  the  building  in  a  horizontal  direction,  so 
that  the  structure  may  be  taken  as  being  under  the  same 
conditions  as  a  uniformly  loaded  beam,  fixed  at  one  end 
and  with  the  other  end  free.  If  this  were  actually  the  case 
with  a  steel  beam,  we  should  make  the  depth  of  the  beam 
such  that  it  would  deflect  less  than  the  amount  necessary 
to  crack  the  plaster.  If  the  beam  were  supported  at  both 
ends,  this  depth  would  be  one  twentieth  of  the  span. 

The  lengths  under  these  two  conditions,  to  secure  the 
same  deflections,  must  bear  the  relation  one  to  the  other  as 
0.57  to  1. 


WIND  BRACING.  l6l 

If,  then,  we  have  an  office  building  or  any  skeleton 
structure  25  ft.  wide,  and  make  the  height  twenty  times  the 
width,  the  building  would  be  500  ft.  high,  and  reducing 
this  in  the  above  ratio,  we  have  285  ft. 

This  height  would  give  a  theoretical  deflection  of  some 
8  in.  or  9  in.,  which  would  throw  the  centre  of  gravity  of 
the  upper  wall  beyond  the  outer  edge.  The  maximum 
allowable  deflection  would  be  about  2|  in.  or  3  in.,  and  this 
would  give  a  height  of  from  70  to  95  feet. 

The  load  effect  on  a  uniformly  loaded  cantilever  is  four 
times  that  for  a  uniformly  loaded  beam  supported  at  both 
ends.  If  we  work  on  the  assumption  that  the  building  is 
analogous  to  the  cantilever  beam,  and  make  its  height  one 
fourth  as  great  as  we  would  if  it  were  supported  at  both 
ends,  we  should  have  the  depth  to  the  length  about  as 
1  to  5.    This  would  give  a  height  of  125  feet. 

Some  recent  experiments,  however  (see  Engineering 
Neivs,  March  3,  1894),  on  the  deflections  of  tall  skeleton 
construction  buildings  in  Chicago,  tend  to  show  that  any 
actual  deflections  in  well-designed  and  carefully  con- 
structed buildings,  under  very  heavy  winds,  are  far  less 
than  any  theoretical  assumptions.  Two  sets  of  tests  were 
made,  one  on  the  Monadnock  Building  of  seventeen  stories, 
and  the  other  on  the  Pontiac  Building  of  fourteen  stories. 
Observations  were  made  with  transits  set  in  sheltered  posi- 
tions, and  these  observations  were  checked  by  means  of 
plumb-bobs,  suspended  in  the  stair-wells  from  the  top  floor. 

The  vibrations  in  the  Monadnock:  Building  from  west 
to  east,  or  in  its  narrow  direction,  were  from  \  in.  to  i  in. 
The  plumb-bob  test,  however,  showed  the  greatest  variation 
to  be  in  a  north  and  south  direction,  or  longitudinally  ;  but 
as  the  walls  in  three  of  the  four  separate  divisions  of  this 
building  are  of  solid  brickwork,  from  3  ft.  to  6  ft.  in  thick- 
ness, and  the  length  is  several  times  the  breadth,  it  is  diffi- 


162 


ARCHITECTURAL  ENGINEERING. 


cult  to  believe  that  any  actual  longitudinal  deflection  could 
be  detected. 

In  the  transverse  deflections  the  transits  showed  a 
greater  deflection  in  the  veneer  portion  of  the  building 
than  in  the  more  solid  parts,  as  would  very  naturally  be 
expected.    The  time  of  a  complete  vibration  was  two 

seconds. 

The  experiments  on  the  Pontiac  Building,  which  is  of 
the  veneer  type,  compared  very  closely  with  those  on  the 
Monadnock  Building,  except  that  the  amplitude  of  the 
vibration  was  less  in  the  former  building,  due  to  its  some- 
what more  sheltered  position.  The  same  peculiarity  of  an 
apparently  greater  longitudinal  vibration  was  noticed  here 
also.  The  wind  was  from  the  northwest,  and  registered 
eighty  miles  per  hour. 


CHAPTER  IX. 
PARTITIONS— ROOFS— MISCELLANEOUS. 

PARTITIONS. 

Most  of  the  partitions  now  placed  in  Chicago  office 
buildings  are  made  from  the  same  character  of  hollow  tile 
as  is  used  in  the  floors  and  around  the  columns,  except  that 
a  soft  tile  is  almost  invariably  used  to  allow  the  driving  of 
nails  in  placing  the  door-frames  and  transom-lights.  Tile 
blocks  are  used  in  this  construction,  varying  in  thickness 
from  2  in.  to  6  in.,  but  the  4-in.  blocks  are  generally  used. 
They  may  be  either  square  or  brick-shaped,  and  are  fre- 
quently clamped  together,  but  are  always  laid  to  break 
joint.  At  all  openings  in  the  partitions  wood  frames  are  set 
to  stiffen  the  jambs,  and  to  afford  grounds  for  the  plastering, 
as  well  as  to  serve  for  the  attachment  of  the  architraves. 
The  plastering  is  applied  directly  to  the  tile  surface. 

These  partitions  may  be  readily  torn  down  and  shifted 
to  suit  the  tenant,  without  injuring  the  construction  of  the 
floors  or  walls.    They  are  never  used  to  sustain  loads. 

An  effective  partition  which  has  been  used  quite  exten- 
sively, consists  of  metallic  lathing  wired  to  light  channel- 
irons,  spaced  as  studs.  Each  side  is  then  plastered,  making 
a  partition  only  2  in.  thick.  This  type  of  partitions  was 
adopted  in  the  Armour  school  and  in  the  Dexter  office 
building  in  Chicago. 

Another  method  is  to  use  i^-in.  I  beams  spaced  as  studs 

2  ft.  on  centres.    The  spaces  between  these  supports  are 

163 


164 


ARCHITECTURAL  ENGINEERING. 


filled  in  with  scratch-coat  mortar,  and  a  coat  of  plaster- 
ing may  then  be  given  each  side.  Ii  either  of  these  systems 
of  metal  studs  is  used,  a  strong  solution  of  alum-water 
should  be  given  the  rough  coat  of  plastering  to  prevent  the 
staining  of  the  finished  plaster. 

ROOF  CONSTRUCTION. 

The  roof  construction  in  such  classes  of  buildings  as  are 
here  being  considered,  should  be  as  thoroughly  fire-proof  as 
any  other  part  of  the  structure.  This  is  secured  through 
the  use  of  tile  arches,  as  in  the  floors,  or  by  means  of  book- 
tile  supported  on  T  irons,  placed  about  18  in.  centres.  The 
T  irons  are  supported  on  I-beam  purlins,  and  if  this  type  is 
employed  care  must  be  taken  to  see  that  such  a  form  of 
book-tile  is  used  as  will  effectually  protect  the  under  sur- 
faces of  the  T  irons.  A  common  method  has  been  to  place 
the  book-tile  on  the  flanges  of  the  T  irons,  thus  leaving  the 
lower  surface  of  the  T's  with  a  coating  of  plaster  only. 
Book-tile  are  now  made  which  project  below  the  metal 
work,  as  do  the  floor  arches,  thus  offering  a  coating  of  clay 
as  protection  against  heat  (see  Fig.  105). 


Fig.  105, 

Tile  arches  of  the  segmental  pattern  are  often  used  in 
roof  construction,  and  the  whole  is  then  covered  with  a 
layer  of  concrete  which  receives  the  composition  roofing 
(see  Fig.  57).  The  supporting  girders  and  purlins  should 
also  be  covered,  either  with  special  forms  of  tile  blocks  or 
slabs,  or  else  with  expanded  metal  lath  to  receive  a  thick 
coat  of  cement  plaster. 

Great  care  should  be  taken  to  see  that  all  spaces  between 


i 


PAR  Tl  TIONS— ROOFS— MISCELLANEO  US,  l6$ 

roofs  and  suspended  ceilings  are  rendered  fire-proof  in  all 
their  parts,  that  the  spread  of  unseen  fire  may  be  made  im- 
possible. Much  may  be  done  through  a  judicious  use  of 
metallic  lath  secured  to  a  light  iron  framework,  in  the 
innumerable  instances  where  a  masonry  or  tile  protection 
becomes  impossible. 

SUSPENDED  CEILINGS. 

Such  ceilings  are  usually  made  of  book-tile  or  of  a  thin 
fire-clay  tile  supported  by  light  T  irons.  Ceiling  tile  is  often 
made  not  over  J  in.  in  thickness,  with  grooved  edges  that 
fit  into  i  X  i  inch  T  irons,  spaced  12  inch  centres,  which  are 
supported  in  turn  by  3  in.  T's  hung  from  the  roof  purlins. 

FURRING  TILE, 

to  take  the  place  of  the  wood  and  lath  furring  used  in  ordi- 
nary construction,  is  employed  to  prevent  the  penetration 
of  the  moisture  through  the  exterior  walls.  These  tiles  are 
made  similar  to  the  partition  tile,  and  should  always  be  pro- 
vided with  an  air-space,  to  insure  a  circulation  of  air,  that 
the  injurious  effects  of  damp  walls  upon  the  interior  finish 
may  be  overcome. 

FIRE-PROOF  VAULTS. 

The  old  system  of  building  brick  vaults  in  tiers  is  not 
followed  in  the  modern  office  building.  The  vaults  are  now 
built  of  tile  and  placed  as  may  be  desired  according  to  each 
floor  plan,  much  as  the  tile  partitions.  They  are  not 
usually  shifted,  but  should  it  be  required,  the  operation 
would  in  no  way  affect  the  floor  or  load-bearing  construc- 
tion. The  tile  walls  should  be  of  considerable  thickness, 
with  at  least  two  air-spaces,  and  the  top  should  also  be 
made  of  two  thicknesses  of  tile  in  case  the  vault  does  not 
run  to  the  ceiling. 


ARCHITECTURAL  ENGINEERING. 


STAIRWAYS  AND  ELEVATOR  ENCLOSURES. 

The  stairways  are  usually  made  of  cast  risers,  strings, 
and  newel-posts,  with  wrought  railings  and  wooden  or 
polished  bronze  or  brass  hand-rail.  All  exposed  parts  of 
the  risers  and  strings  are  generally  specified  to  be  panelled 


Fig.  106  Main  Entrance  and  Elevator-hall,  Marquette  Building. 

and  ornamented  as  per  detail  drawings,  and  provided  with 
lugs  and  flanges  to  receive  the  marble  treads  and  plat- 
forms.   The  metal-work  for  the  stairways  and  the  elevator 


PA  R  TIT  IONS — ROOFS — MISCELLA  NEO  US.  167 

guards  or  enclosures  are  heavily  electroplated  in  brass,  cop- 
per, or  bronze.  An  aluminium  finish  was  tried  in  the  newer 
portion  of  the  Monadnock  Building,  Chicago,  but  it  has 
tarnished  very  badly.  Fig.  106  shows  the  main  entrance-hall 
to  the  Marquette  Building,  serving  as  a  good  illustration  of 
the  decorative  treatment  which  may  be  given  the  columns 
and  exposed  or  sunken  girders  in  the  ceiling.    Fig.  107 


Fig.  107.  —  Entrance-hall,  New  York  Life  Insurance  Building. 

shows  the  main  entrance  to  the  New  Vork  Life  Insurance 
Building,  with  the  walls,  ceiling,  and  stairs  finished  in 
Italian  marble  and  the  floor  of  mosaic. 


i68 


A  R  CHITE C T URA  L  ENGINEERING. 


The  main  stairway  and  entrance-hall  to  the  Fort  Dear- 
born Building  are  given  in  Fig.  to8. 


•  .JHWEY  &MUNDIE  'ARCHITECTS  ■ 


Fig  i 08.— Entrance-hall,  Fort  Dearborn  Building. 
COLUMN-SHEETS. 

Before  the  column-sheets  may  be  started  it  is  necessary 
that  all  loads  occurring  in  the  structure  be  definitely  settled. 
These  loads  include,  as  suggested  in  the  previous  chapters, 
the  weights  of  all  structural  material  (floors,  roof,  piers, 
spandrels,  and  the  like),  besides  wind,  snow,  elevator,  and 
tank  loads.  The  column-sheets  may  then  be  started,  forming 
a  tabulated  list  of  all  the  loads  transferred  to  the  footings 
through  the  columns.  From  these  sheets  may  be  seen  the 
approximate  load  that  each  column  must  carry  at  any  floor, 
starting  with  the  upper-story  columns,  supporting  the  roof 
load  only,  and  adding  in  the  loads  at  the  successive  floors 
down  to  the  foundations.    The  column  weight  itself  is  first 


/ 

PARTI  TIONS — ROOFS — MISCELLA  NEO  US.  1 69 

assumed,  and  then  corrected,  after  the  proper  section  is 
obtained. 

The  column-sheet  used  in  the  Masonic  Temple  calcula- 
tions was  as  follows : 


Roof. 

Column  1. 

Column  2. 

Load 
on  Column. 

Load 
on  Footing. 

Load 
on  Column. 

Load 
on  Footing. 

Total  

P4 
O 
O 

X 
H 
O 

The  column-sheet  used  in  the  Venetian  Building  was 
made  as  in  the  accompanying  table: 


Column  1. 

Roof. 

Attic. 

12th 
Floor. 

Base- 
ment. 

Total. 

Total  

Wind  Loads. 

Column  2. 

» 

Etc. 

17°  ARCHITECTURAL  ENGINEERING. 


The  following  column-sheet  is  to  be  recommended  as 
combining  all  requisites  in  a  tabulated  statement: 


Column  i. 

Column  2. 

Load 
on  Column. 
Concentric. 

Load 
on  Column. 
Eccentric. 

Load 
on  Footing. 

Roof. 

TTM  —  1  3 

Total  

Area  required  for  col. . . 

sq.  in. 

sq.  in. 

Foot'g  area 

sq.  ft. 

Load 
on  Column. 
Concentric. 

Load 
on  Column. 
Eccentric. 

Load 
on  Footing. 

i6th  Floor. 

Etc. 

The  final  loads  on  the  basement  columns  taken  from  these 
sheets  will  show  the  loads  for  which  the  footings  themselves 
must  be  figured,  while  the  final  loads  on  the  footings  will 
give  the  weights  for  which  the  clay  areas  must  be  propor- 
tioned. 


CHAPTER  X. 


FOUNDATIONS. 


No  part  of  the  work  of  the  engineer  requires  more  care 
and  skill  than  the  design  and  execution  of  the  foundations. 
"  Where  it  is  necessary,  as  so  frequently  it  is  at  the  present 
day,  to  erect  gigantic  edifices — as  high  buildings  or  long- 
span  bridges — on  weak  and  treacherous  soils,  the  highest 
constructive  skill  is  required  to  supplement  the  weakness  of 
the  natural  foundation  by  such  artificial  means  as  will  enable 
it  to  sustain  such  massive  and  costly  burdens  with  safety  " 
(Baker).  And  nowhere  is  this  more  true  than  in  Chicago, 
where  it  is  almost  impossible  to  penetrate  to  bed-rock  with 
any  degree  of  practicability,  and  where  the  soil  underlying 
the  city  consists  of  blue  clay  (below  a  soft  loam  or  quick- 
sand) at  about  12  or  14  feet  below  the  sidewalk  grade,  and 
thence  down  to  a  bed-rock  of  limestone  from  40  to  80  feet 
below  the  street  level.  The  clay  is  hard  and  firm  in  the 
upper  strata,  but  becomes  soft  and  yielding  as  it  descends, 
often  containing  pockets  of  spongy  material,  thus  necessi- 
tating borings  for  reliable  information  of  particular  locali- 
ties. Borings  have  been  extensively  made,  both  by  private 
parties  and  by  the  government,  resulting  in  an  allowance  of 
from  1^  to  2  tons  per  sq.  ft.  on  the  clay,  with  due  consider- 
ation for  proper  settlement.  Baker  states  as  follows  on 
this  subject :  "  The  stiffer  varieties  of  what  is  ordinarily 
called  clay,  when  kept  dry,  will  safely  bear  from  4  to  6  tons 
per  sq.  ft.,  but  the  same  clay,  if  allowed  to  become  saturated 
with  water,  cannot  be  trusted  to  bear  more  than  2  tons  per 


1/2 


ARCHITECTURAL  ENGINEERING. 


sq.  ft.  At  Chicago  the  load  ordinarily  put  on  a  thin  layer  of 
clay  (hard  above  and  soft  below,  resting  on  a  thick  stratum 
of  quicksand)  is  to  2  tons  per  sq.  ft.,  and  the  settlement, 
which  usually  reaches  a  maximum  in  a  year,  is  about  i  in. 
per  ton  of  load." 

Unequal  settlement  is  thus  the  great  evil  that  must  be 
guarded  against,  for  settlement  will  come,  slowly  but  surely, 
and  in  all  good  designs  it  is  provided  for  in  the  start  by 
making  the  structure  some  3  in.  to  5  in.  higher  than  its  final 
level.  The  evil  of  unequal  settlement  can  hardly  be  better 
exemplified  than  in  the  case  of  the  United  States  Govern- 
ment Post  Office  and  Custom  House  in  Chicago,  built  in 
1877,  and  now  about  to  be  replaced  by  a  new  one.  The 
foundations  consist  of  a  continuous  sheet  of  concrete,  made 
in  different  layers,  but  altogether  3  ft.  6  in.  thick.  Some 
portions  of  the  building  were  extraordinarily  heavy,  others 
comparatively  light,  but  the  Washington  architects  thought 
the  concrete  sufficient,  even  though  there  were  bad  sloughs 
under  the  building.  But  it  has  proved  a  most  dismal 
failure,  and  even  a  menace  to  life  and  limb.  It  has  settled 
nearly  24  in.  in  places,  and  a  dropping  of  some  part  of  the 
structure  is  no  unusual  occurrence.  After  but  eighteen 
years  of  service  this  example  of  government  architecture 
and  engineering  has  been  known  as  "  The  Ruin  "  in  Chi 
cago  and  vicinity. 

The  investigation  of  the  compressibility  of  the  soil  leads 
to  the  conclusion  that,  if  we  wish  to  procure  uniform  settle- 
ment, all  parts  of  the  foundation  areas  must  be  exactly  pro- 
portioned to  the  loads  they  have  to  carry.  Examples  are 
not  lacking,  in  Chicago  and  elsewhere,  of  the  actual  crush- 
ing of  light  piers,  when  alternating  with  heavy  ones,  be- 
cause,  proportionately,  the  lighter  piers  had  too  great  a  foot- 
ing area.  In  the  Mills  Building  in  New  York  City  the 
mullions  in  the  lower  floors  of  the  building  and  over  the 


FO  UND  A  TIONS.  1 7  3 

light  foundations  were  seriously  damaged  and  even 
crushed,  because  they  were  not  strong  enough  to  force 
down  the  lighter  piers  of  too  large  an  area,  as  fast  as  the 
heavy  piers  were  settling. 

The  footings  themselves  must  be  of  sufficient  strength 
to  distribute  the  applied  loads  over  the  requisite  area ;  in 
this  way  only  can  satisfactory  results  be  obtained. 

The  arrangement  of  independent  piers  was  first  advo- 
cated in  Chicago  by  Frederick  Bauman,  in  a  pamphlet 
published  by  him  in  1872,  entitled  "  The  Method  of  Con- 
structing Foundations  on  Isolated  Piers,"  and  this  method 
has  certainly  been  brought  to  a  high  degree  of  perfection 
by  the  engineers  of  Chicago.  The  rapid  development  of 
foundations  is  well  exemplified  by  the  great  change  in 
methods  employed  at  the  site  of  the  Woman's  Temple.  In 
1890  the  lot  where  this  building  now  stands  was  bought  by 
the  present  owners.  Extensive  masonry  foundations  had 
previously  been  built  here  for  a  structure  that  was  never 
erected,  and  upon  the  preparation  of  plans  for  the  Temple, 
the  first  thing  done  was  to  remove  these  massive  masonry 
piers  at  a  cost  of  many  thousands  of  dollars.  The  old  sys- 
tem consisted  of  stone  piers  made  of  successive  layers  of 
large  stones,  stepping  out  until  a  sufficient  base  was  ob- 
tained. One  of  these  newer  "  raft"  footings  is  here  given, 
and  also  one  of  the  old  masonry  type  (Figs.  109,  no). 

The  objections  to  these  old  piers  were  many  :  they  were 
bulky,  occupying  too  much  space  ;  they  were  heavy  and 
costly  as  regarded  the  time  necessary  for  building ;  and  the 
allowable  offsets  of  the  masonry-work  seriously  limited  the 
load-bearing  surface  of  the  clay. 

These  piers  in  the  Woman's  Temple  were  all  underlaid 
with  a  bed  of  concrete,  resting  on  the  clay  stratum  about 
10  ft.  below  street  grade.  A  comparison  of  some  of  the 
above  points  may  be  made  as  follows: 


174 


A  R  CHITE  C  T  URA  L  ENG  IN  EE  RING. 


I.  Space. 

i st.  Top  of  concrete  to  bottom  of  casting  =  i'  8". 

2^        <<       "  <<  "  "         "  "         —  y'  Qr/ 


Or,  comparing  the  parts  above  the  common  bed  of  concrete, 
ist  =  217  cu.  ft.,    2d  =  691  cu.  ft. 
This  point  of  space  is  a  very  important  one,  as  has  been 
before  mentioned,  since  basement-space  is  now  quite  as  valu- 

I 


!  M- 
H  


WMSm*^  Hfr    TTT?     T^T  T  f  I 


Fig.  109. 


i  Liar 


/i>" 


1 


Fig.  iio. 


able  as  any  office-space,  for  use  as  restaurants,  cafes,  or  for 
the  large  boiler  and  electric-light  plants  necessary.  Indeed, 
it  is  of  frequent  occurrence  to  extend  the  basement-space 


I 

FO  UNDA  TIONS.  1 7  5 

out  under  the  sidewalks  and  even  alleys.  Thus,  to  gain 
cellar-room,  the  foundation  must  either  be  lowered  or  made 
thinner.  The  first  has  been  ruled  out  of  Chicago  practice, 
because  it  has  been  clearly  demonstrated  that  the  less  the 
clay  stratum  is  broken,  the  more  uniform  and  satisfactory 
the  settlement  will  be.    Hence  the  present  details. 

II.  Weight. — Rating  the  masonry  at  150  lbs.  per  cu.  ft., 
concrete  at  140  lbs.,  and  allowing  44  cu.  ft.  for  the  steel  in 
No.  1,  the  weights  are  : 

No.  1  =  103,000  lbs. 
No.  2  =  261,000  lbs. 

The  load  for  this  foundation  is  800,000  lbs.  and  the  saving 
in  weight,  through  the  use  of  the  raft  foundation,  is  thus 
sufficient  to  allow  an  additional  story,  without  adding  to 
the  load  on  the  clay.  On  large  foundations  this  difference 
is  still  greater.  In  the  case  here  assumed  the  103,000  lbs. 
is  about  13  per  cent  of  the  load  carried,  but  in  some 
cases,  under  very  heavy  loads,  it  has  been  found  to  run  as 
high  as  20  per  cent  (see  "  Steel  Rail  Foundations,"  Engineer- 
ing News,  August,  1 891). 

This  saving  in  weight  is  one  of  the  factors  that  makes 
our  highest  buildings  possible,  and  even  the  "  sky- 
scrapers "  are  not  loading  the  clay  as  severely  as  some  of 
the  older  structures.  When  the  foundations  of  the  old 
masonry  building  were  torn  out  to  make  room  for  the  new 
,  Reliance  office  building,  the  clay  was  found  to  be  loaded 
to  2  tons  and  over  per  sq.  ft.  for  a  five-story  building, 
while  "  The  Fair  "  Building  is  loaded  to  2850  lbs.  only,  for 
a  sixteen-story  modern  structure. 

III.  Cost. — In  general,  the  cost  of  stone  foundations  will 
be  less  than  iron  ones,  but  considering  the  renting-space  in 
basements,  this  difference  will  be  quickly  made  up  where 
the  latter  are  used. 


176 


ARCHITECTURAL  ENGINEERING. 


IV.  Time. — In  the  time  required  for  building  opera- 
tions the  new  foundations  are  greatly  superior,  as  rails  and 
beams  are  easily  obtained  and  cheaply  handled. 

V.  Load-bearing  Area. — As  to  the  fifth  point,  stone 
foundations  under  side  walls  frequently  cannot  step  out 
sufficiently  to  get  the  proper  bearing  area  without  project- 
ing into  the  next  lot.  But  with  iron  we  can  combine 
several  footings,  or  use  cantilever  foundations,  thus  secur- 
ing the  desired  results. 

As  may  be  seen  by  Fig.  109,  the  new  type  of  founda- 
tions consists  first  of  a  layer  of  concrete,  about  2  ft.  thick, 
upon  which  come  layers  of  I  beams  or  rails,  each  layer 
laid  transversely  to  those  just  below  or  above.  The  spaces 
between  the  rails  are  rammed  tight  with  concrete,  which 
preserves  the  iron  from  the  action  of  air  and  water. 

It  is  the  judgment  of  the  best  engineers  that  the  area 
of  the  foundations  on  the  clay  should  be  proportioned  to 
the  dead  loads  only,  and  not  to  theoretical  or  occasional 
loads.  Whenever  live  loads  have  been  figured  on  both  the 
interior  columns  and  on  the  columns  in  the  exterior  walls, 
the  exterior  columns  have  always  been  found  to  settle 
more,  from  the  fact  that  the  live  load  forms  a  larger  per- 
centage of  the  interior-column  loads  than  of  the  wall- 
column  loads.  Experience  has  also  shown  that  after  the 
clay  has  been  compressed  by  a  load  of  3000  lbs.  per  sq.  ft., 
and  allowed  several  months'  repose,  no  very  perceptible 
addition  to  that  compression  will  result  without  a  material 
addition  to  the  load.  So  that  it  is  good  practice  to  neglect 
live  loads  on  the  clay  for  hotels,  office  buildings,  or  lightly 
loaded  retail  stores.  In  warehouses,  however,  or  in  build- 
ings carrying  very  heavy  permanent  or  shifting  floor 
loads,  or  machinery  in  motion,  the  change  of  loads  and 
the   jarring  increase  the  compression  of   the  clay  very 


FO  UNDA  TIONS.  I  7  7 

largely.  Hence  we  must  make  extra  allowances  in  such 
instances. 

In  all  cases  where  live  loads  have  been  figured  on  the 
columns,  consistency  requires  that  whatever  loads  have  been 
figured  on  basement  columns,  must  be  figured  on  the 
metal  in  the  foundations ;  or  the  clay  areas  are  proportioned 
for  dead  loads  only,  while  the  strengths  of  the  foundations 
themselves  are  figured  for  dead  -\-  some  live  load.  But,  as 
before  said,  many  of  the  best  buildings  have  entirely  dis- 
regarded live  loads  on  the  footings.  W.  L.  B.  Jenney 
advocates  as  follows:  In  hotels,  office  buildings,  and  retail 
stores  neglect  the  live  loads  on  the  footings,  but  figure 
them  in  heavy  warehouses,  machinery  plants,  etc.  Where 
much  pounding  occurs,  as  in  machinery  in  motion,  use 
double  the  weight  as  dead  load  that  we  figure  for  live  load. 

In  "  The  Fair  "  Building,  where  a  large  quantity  of  mer- 
chandise is  stored,  and  the  aisles  are  constantly  filled  by 
throngs  of  people,  the  following  system  was  used :  The 
floor-beams  carry  all  the  dead  -f-  live  loads,  the  girders 
carry  the  dead  load  -f-  90  per  cent  of  the  live  load,  while 
any  one  column  carries  a  percentage  of  the  sum  of  the 
live  loads  of  all  the  stories  above  that  column  -f-  the  total 
dead  load.  The  percentage  of  live  load  is  given  in  the 
last  column  of  the  accompanying  table : 


Column.                    Live  load  on  beams.  Per  cent  for  column. 

Attic    100  per  cent. 

16th  story  75  lbs.  90     "  " 

15th     "  75  "  Syi   "  " 

14th     "  75  "  771   -  " 

13th     "  75  "  72I   "  " 

    Decrease  of  2\  per 

    cent  in  each  story. 

6th  story  75  ibs.  55    per  cent. 

5th  130  "  52$  " 

Basement  130  40     "  " 


i78 


ARCHITECTURAL  ENG INEER1NC . 


No  live  load  was  figured  on  the  clay  area,  but  the 
allowable  pressure  per  square  foot  was  taken  at  a  very  con- 
servative figure — 2850  lbs. 

The  first  use  in  Chicago  of  iron  rails,  in  connection  with 
masonry  or  concrete  footings,  occurred  in  the  Montauk 
Block,  by  Burnham  &  Root,  architects.  The  old  method 
of  pyramidal  foundations  of  dimension  stones  was  used 
with  a  concrete  base  18  in.  thick.  Iron  rails  were  built  into 
this  concrete  to  obtain  a  larger  offset  than  could  otherwise 
have  been  obtained. 

At  first  old  rails  were  employed  in  these  foundations, 
but  now  practice  demands  as  reliable  material  in  this  por- 
tion of  the  metal-work  as  in  any  other.  Steel  rails  at  75  lbs. 
per  yd.  are  generally  used  unless  steel  beams  are  required. 
Ordinarily,  rails  are  cheaper  than  beams ;  more  iron  is 
required,  but  at  less  cost  than  in  beams.  The  concrete,  too, 
is  easier  to  ram  between  the  rails,  and  the  webs  are  always 
thick. 

Under  very  heavy  loads,  or  long  spans,  beams  become 
necessary,  10  in.  to  20  in.  I  beams  being  frequently  used. 
Only  the  projecting  portions  are  strained  as  beams,  hence 
the  place  for  beams  is  at  the  top  of  the  pile — the  larger  the 
proportion  of  iron  or  steel  uncovered  the  more  economical 
the  foundation.  20,000  lbs.  and  16,000  lbs.  have  been  used 
for  fibre  strains  in  steel  beams  and  iron  rails,  though  the 
new  Chicago  ordinance  limits  the  fibre  strain  to  14,000  lbs. 
and  11,000  lbs.  per  square  inch.  In  the  Old  Colony  Build- 
ing the  steel  beams  in  the  foundations  are  strained  to  a  fibre 
strain  of  14,000  lbs.  under  the  dead  weight  of  the  building 
alone,  while  the  maximum  dead  plus  live  loads  induce  a 
fibre  strain  of  21,000  lbs.  per  sq.  in.  of  extreme  fibre.  The 
Carnegie  strike  at  the  time  of  building  precluded  the  possi- 
bility of  obtaining  heavier  beams  than  15-in.  90-lb.  I  beams, 
so  the  strain  was  allowed  under  the  press  of  circumstances. 


FO  UND  A  T10NS.  I  79 


RAIL  FOOTINGS. 


The  raft  footings  as  first  employed  were  made  of  rails 

only,   the   usual  method   of  figuring   being   as   follows : 

The  number  of  square  feet  of  footing   required  equals 

load  on  column  .  .  .      .  .  . 

 =  7  -T-.     Multiply  the  result  by  250 

pounds  per  sq.  it.  on  earth  J  J  * 

(equals  approximate  weight  of  footing  per  square  foot),  add 
to  the  original  load,  and  refigure.  The  layers  are  then 
laid  off,  the  projection  of  any  layer  beyond  the  one  imme- 
diately above  being  always  3'  o"  or  less.  The  moments  on 
the  projecting  portions  of  the  layers  are  then  found,  and 
these  moments,  divided  by  the  allowable  bending  moment 
per  rail,  usually  taken  at  12,500  foot-lbs.,  give  the  number 
of  rails  required  in  the  different  courses.  One  extra  rail 
is  usually  added  to  each  layer  as  a  matter  of  safety. 

The  following  table  gives  the  properties  of  the  rails  from 
the  North  Chicago  Rolling  Mills.  The  75-lb.  rails  are 
most  commonly  used. 


No. 

Weight. 

Height. 

Base. 

u. 

I. 

R. 

M. 

/—  16,000. 

6504 

65  lbs. 

4f" 

4*" 

15.86 

6.86 

9,150 

750I 

75  " 

21  .OO 

8.30 

11,070 

7503 

75  " 

4f 

4t 

21 .66 

9-37 

12,500 

8001 

80  " 

5 

5 

02  1 
2  6? 

26.36 

9-99 

13,320 

8501 

85  " 

5 

4f 

96 

28 

27.32 

10.41 

/3,88o 

8502 

85  " 

5t^ 

5  . 

28 

29.22 

11 . 13 

14,840 

8503 

85  " 

5 

5 

2^2 

25.38 

10.03 

i3,37o 

The  table  following  is  taken  from  the  footings  of  the 
Great  Northern  Hotel,  giving  the  loads  on  columns,  areas 
of  footings,  and  the  calculated  weights  per  square  foot  of 
the  rails  and  the  concrete  in  the  footings.  All  rails  were 
75-lb.  rails,  No.  7503  in  the  previous  table.  The  bottom 
courses  of  all  footings  were  of  concrete,  12"  thick,  ex- 
tending 6"  beyond  the  lower  course  of  rails,  but  the 
weights  of  these  concrete  courses  are  not  included  in  the 


l80  ARCHITECTURAL  ENGINEERING. 

following.  Cast  shoes  4'  o"  X  4'  o"  were  used  under  all  the 
columns.  The  concrete  was  figured  as  weighing  125  lbs. 
per  cubic  foot. 


Weight  per  sq.  ft. 

Load  on  Col. 

Area  of  Footing,  sq.  ft. 

Rails. 

Concrete. 

415.470 

12'    X  1  if  =  141' 

49 

83 

433.440 

10    X  I4i  =  T46 

58 

60 

435,820 

9     X  i6{  =  146 

77 

83 

461,100 

12    X  13    =  156 

42 

•  80 

496,240 

10    X  i6£  =  163 

79 

91 

526,850 

I2f  X  14    =  178 

66 

82 

531,740 

13    X  Mi  =  185 

60 

78 

571,360 

I3i  X  14?  =  192 

67 

74 

595,92° 

12^    X  16     =  200 

67 

88 

621,560 

13    X  16    =  208 

60 

94 

637,240 

I3i  X  16    =  214 

68 

68 

666,000 

15    X  15    =  225 

66 

105 

672,000 

13    X  I7i  =  228 

67 

93 

BEAM  AND  RAIL  FOOTINGS. 

The  next  step  made  in  the  development  of  the  raft  foot- 
ings was  in  the  use  of  I  beams  for  the  upper  course  or 
courses.  Fig.  11 1  shows  a  foundation  which  was  figured  as 
follows  (see  Engineering  News,  August,  1891): 

The  column  load  was  1,166,000  lbs.  The  allowable 
pressure  per  square  foot  on  the  clay  was  taken  at  3,000  lbs., 
giving  a  footing  22'  8"  X  if  3".  The  lower  layer  of  con- 
crete was  18"  thick,  projecting  8"  beyond  the  lower  course 
of  rails.  Fifteen-inch  steel  beams  were  used  in  the  top 
course,  weighing  50  lbs.  per  foot.  The  allowable  moment 
on  each  beam  equalled  117,700  ft.-lbs.  The  remaining 
courses  were  of  steel  rails,  4f"  high  and  4f"  base,  75  lbs. 
per  yard  weight,  with  an  allowable  moment  of  12,100  ft.-lbs. 
per  rail. 

In  the  upper  course,  as  many  beams  are  used  as  the 
space  under  the  column  casting  will  allow.  The  project- 
ing arms  must  therefore  be  determined.  The  total  length 
of  the  I  beams  so  found  will  fix  the  width  of  the  second 


/ 

FO  UND  A  TIONS.  1 8 1 

course  from  the  top,  and  the  projecting  arms  must  be  found 
for  this  course  as  in  the  first  case. 

The  arms  of  the  lower  two  courses  are  fixed  by  the 


Fig.  hi.— Beam  and  Rail  Footing  from  "The  Fair"  Building. 

lengths  of  the  upper  ones,  and  by  the  dimensions  of  the  clay 
area ;  hence  the  question  is,  how  many  pieces  are  required  ? 
The  formulae  used  may  be  derived  as  follows : 
Let  y  —  projecting  arm  in  any  course  ; 
a  =  width  of  supporting  area ; 


182 


ARCHITECTURAL  ENGINEERING. 


I  =  total  load  on  footing  ; 
M  —  bending  moment  on  one  side  of  the  layer. 

Then  the  length  of  beam  or  rail  =  a  -\-  y  -\-  y  =  a  2y. 

ly 

The  total  load  on  y  =  — .  ,  and  since  the  distribution  of 

J  a-\-2y 

the  load  on  every  layer  is  uniform,  we  have 

ly  y  ly1 

M  —  — r —  X  lever  arm  -  = 


a  -\-  2y  2      2{a  -\-  2y)' 

In  calculating  the  lower  two  courses, y  becomes  a  known 

quantity  and  M  an  unknown.    In  the  upper  two  layers  M 

is  given  by  the  number  of  the  beams  used  and  y  is  unknown. 

Considering  now  the  top  course,  under  the  base  casting, 

5'o"  X  5'  o"  in  area,  we  find  that  9  beams  only  can  be  placed 

under  the  casting,  allowing  sufficient  space  between  them 

for  the  ramming  of  the  concrete. 

M  for  each  beam  =  117,700  ft.-lbs.     Hence  M  for  the 

whole  layer  =  9  X  117,700  ft.-lbs.  =  1,059,300  ft.-lbs.  Then 

1,166,000/  ,  .  , 

2(5  -f-  2y)  =  I'°59'300'  whence  y  =  54.     The  length  of 

this  layer  then  becomes  5  -|-  2y  =  15'  . 

For  the  second  course  we  find  that  31  rails  spaced  about 

6"  centres  may  be  placed  under  the  15'  8"  beams.  Closer 

spacing  than  this  may  be  used  if  necessary.    The  load  now 

equals  1,166,000  lbs.  +  the  weight  of  the  top  course  (about 

„    x    _u  1,185,000/ 
19,000  lbs.).   I  hen  2^  _|_  2^  =  375>ioo;  whence  y  =  2  5  . 

The  length  of  the  rails  therefore  =  5'  o"  +  4'  10"  =  9'  \o". 

For  the  calculation  of  the  lower  courses,  we  know  that 
the  area  covered  by  the  bottom  course  is  15'  u/r  X  2i/4//. 
This  leaves  a  projection  of  3/o|-//  for  the  bottom  course,  and 
a  projection  of  2'  10"  for  the  next  to  the  bottom  layer. 

Then  for  the  third  or  next  to  the  bottom  course,  we  have 

*A  =  1,200.000  lbs.  X2|  ft.  x.A  =  =  M 

a  +  2y  2ij- 


M  =  — „  =  343)000  ft  Jbs 


FO  UNDA  TIONS.  1 8  3 

This  moment  requires  19  rails  to  be  used  in  the  layer. 
For  the  bottom  course, 

1,220,000  lbs.  X  3  A"  ft-  X  iff 
c 1 1 

0  12 

This  requires  29  rails,  30  being  used  for  safety. 

It  will  be  noticed  in  the  above  calculation  that  the 
moments  have  been  taken  for  the  projections  of  the  several 
courses  beyond  the  adjacent  supporting  layers  only.  Thus 
in  the  figures  for  the  next  to  the  bottom  course,  as  given 
above,  y  =  2'  10".  If,  however,  the  foundation  be  taken  as 
a  whole,  and  the  bending  moment  on  the  third  course  is 
taken  around  the  edge  of  the  cast  base,  the  same  as  the  top 
course  was  figured,  we  have  /  =  8£  ft.,  or, 

1,200,000  X  8|  X  4tV  c*.  ,l 

M  —  — -  —  —  1,920,000  ft.-lbs. 

21 3 

This  must  be  resisted  by  the  combined  moments  of  the  9"  I 
beams  in  the  top  layer,  and  the  19  rails  in  the  third  layer,  or 
1,059,300  +  229,900=  1,289,200  ft.-lbs.  This  assumption 
leaves  a  difference  ' of  630,800  ft.-lbs.  which  has  not  been 
cared  for. 

The  practice  in  regard  to  the  calculation  of  such  foot- 
ings is  still  an  unsettled  question.  Those  who  used  the  first 
method  claimed  that  the  action  of  the  concrete  filling,  with 
its  tendency  to  bind  the  iron  and  concrete  together,  caused 
the  foundation  to  act  as  a  whole,  and  thus  possess  a 
moment  of  resistance  much  greater  than  the  sum  of  the 
resistance  of  the  individual  layers.  But  in  view  of  the 
uncertainty  of  any  such  assumption,  the  other  method  of 
calculating  all  moments  about  the  edge  of  the  casting 
would  seem  more  logical,  as  well  as  being  on  the  safe  side. 
Both  methods  are  now  being  used  in  Chicago  buildings. 

The  use  of  rails  in  footings  has  been  succeeded  almost 
entirely  by  the  use  of  I-beams  throughout. 


ARCHITECTURAL  ENGINEERING. 


Fig.  112  shows  a  footing  used  in  the  Marquette  Building 
for  a  column  load  of  920,250  pounds. 


5-2Ol-/0OiBs./#ok 

fl  11  Pill  11 11- 


1-f 

I 

'>/4-/5Z-4/L33./4-I0zm 
Col.A/o.  29  -Zoad=$20.250i3s. 
C/9sr  3/iS£  3J6  "x  4-J0 " 

Fig.  112. 


"T 


C/?st3js£s3-6  "x  3jC  0 
low  m  Col  32=406,340ias. 
low o* Col  44=J6/>  790 ios. 

Fig.  113. 


Fig.  113  is  taken  from  the  same  building,  and  is  figured 
for  loads  of  406,340  lbs.  on  column  32,  and  561,790  lbs.  on 
column  44. 

In  determining  the  sizes  of  the  beams  or  rails  in  any 
layer,  care  must  be  taken  to  leave  sufficient  clearance  be- 
tween the  flanges  to  admit  the  concrete  which  must  be 
rammed  in  place.  If  stone,  broken  to  pass  a  f"  ring  be 
specified,  1"  as  a  minimum  between  the  flanges  will  answer. 

In  covering  these  rails  with  concrete  4  inches  of  con- 
crete should  be  left  at  the  ends  and  sides  of  the  rails,  and  1 
inch  on  the  tops.  A  plank  frame  is  made  of  the  same  size 
as  the  concrete  bed,  and  at  the  proper  height  by  the  aid  of 
levels.  After  this  is  filled  another  frame  is  made  for  the 
next  course,  and  so  on.  The  concrete  is  made  of  the  best 
Portland  cement,  usually  1  part  cement  to  4  parts  of  broken 
stone  and  2  parts  of  coarse  sand.  The  concrete  must  be 
well  tamped  between  the  beams,  and  the  whole  exterior 


FO  UND  A  TIONS.  1 8  5 

plastered  with  pure  Portland  cement  mortar,  so  that  no 
metal-work  is  exposed.  A  bed  of  concrete  18"  or  2'  o" 
thick  comes  under  all,  projecting  6"  to  12"  beyond  the  rails. 

COMBINED  FOOTINGS. 

The  raft  foundation  is  particularly  valuable  where  the 
positions  of  loads  in  reference  to  each  other  are  bad.  We 
may  then  use  compound  foundations,  combining  several  by 
means  of  long  beams — as  under  smokestacks,  party-walls,  etc. 

One  of  the  most  delicate  problems  is  the  construction  of 
a  very  heavy  building  by  the  side  of  one  already  completed, 
so  that  the  latter  will  not  suffer  by  settlement,  due  to  the 
additional  weight  of  the  new  building. 

Such  settlement  was  shown  to  a  remarkable  degree  in 
the  Studebaker  Building,  next  to  the  Auditorium,  Chicago. 
The  former  settled  from  10"  to  12 "  from  the  weight  of  the 
latter.  To  obviate  such  settlement  the  old  wall  is  carried 
on  timbers,  supported  at  either  end  by  jack-screws.  The 
new  wall  is  then  put  in,  and,  with  the  new  foundation  which 
is  provided,  settles  gradully.  The  jack-screws  under  the 
old  building  are  turned  as  occasion  requires,  to  keep  the 
old  wall  at  its  proper  level.  This  is  continued  until  all 
settlement  ceases,  when  the  jack-screws  are  removed,  one  by 
one,  and  a  new  wall  is  substituted  under  the  old  building. 

If  access  cannot  be  had  to  the  basement  of  the  old 
building,  or  underpinning,  in  the  manner  above  described, 
is  impossible,  cantilever  foundations  must  be  employed. 
The  old  foundations  must  not  carry  any  additional  weight, 
and  we  cannot  substitute  new  footings ;  hence  the  usual 
type  of  raft  footing  is  used,  but  several  are  combined,  and 
the  centre  of  gravity  of  the  combined  area  coincides  with 
the  centre  of  gravity  of  the  loads.  On  these  footings  come 
high  cast-iron  shoes,  supporting  cantilever  girders  which 
carry  the  columns  and  wall  of  the  new  building,  immedi- 


1 86 


ARCHITECTURAL  ENGINEERING. 


ately  next  to  the  old  one,  and  yet  transferring  all  the  load, 
with  the  attendant  settlement,  away  from  the  lot-line.  The 
first  cantilever  footings  introduced  in  Chicago  were  used 
in  the  Manhattan  and  Rand-McNally  buildings  at  about 
the  same  time.  The  boilers,  etc.,  in  the  basements  of  the 
adjoining  buildings  could  not  be  disturbed  to  allow  the 
introduction  of  new  party-footings,  so  the  cantilever  types 
were  adopted  for  the  new  structures,  and  the  foundations  of 
the  old  ones  were  not  disturbed.  This  method  was  em- 
ployed in  the  Western  Union  Building  in  New  York,  where 


Fig.  114. 


mnr 


30  X 


CASTB/ISf 


Fig.  115. 


a  load  of  286  tons  was  transferred  from  a  corner  to  more 
secure  footings. 

Such  a  combined  footing  may  be  analyzed  as  follows: 


FOUNDATIONS. 


IS/ 


Taking  Fig.  114  as  a  plan,  and  Fig.  115  as  an  elevation,  the 
line  of  flexure  of  the  15"  I  beams  will  be  as  in  Fig.  116.  To 
find  the  maximum  bending  moment  on  these  beams  we  must 


Fig.  116. 

compute  the  various  bending  moments  and  compare.  The 
bending  moment  will  be  maximum  when  the  shear  =  o.  In 
this  case  there  are  five  such  sections,  as  shown  by  the  line 
of  flexure  ;  hence  we  must  compute  the  moment  at  each 
point  to  find  the  greatest.  The  moments  under  the 
columns  will  be  +,  causing  convexity  downward,  while 
the  moments  between  the  columns  are  — ,  causing  con- 
vexity upward.    Fig.  117  may  then  be  used. 


Y-d—k  — 

!       J? . 


t 


^  \  -sd- 

■72  

m 


—  *a^-m->. 

nil?  ' 


t  M  1 1 1 1 1 1  l\ t  f  t  1 1 1 1  h  1 1 

S        P<*\  i  i  1 


 *Jfj 



 jts  —  - 




'4 


— H 


Fig.  117. 


To  find  the  distance  of  the  centre  of  gravity  of  the  loads 
from  the  left  end  we  have 

X~  p+pi  +  p2 


j   ,       P  Px  P2  ,    P  +  Px  +  P, 

Let     5=*'   i=*»  T=A-  and  / 


The  distances  from  the  left  end  of  the  beams  to  the  points 


1 88  ARCHITECTURAL  ENGINEERING. 

where  5  =  o,  or  the  distances  xx>  x%i  xz,  xKy  and  xi}  are  then 
found  to  be  as  follows: 

mp 

xxp%  =  {xx  -  m)p,    or    xx  = 


P  —  Pz 
P 

**Pt  =  p*  or  **  =  -t  ; 

*.A  =  ^+ [*.-(*  +  *  +  »)]*,>  or  *,  =  v       tZ-p   ; 

*<P,  =  P  +  P„    or    *4  =  -^-^; 

*6 /3  =  P+Pl+[xh-(m  +  a  +  n+al  +  q)]p2 , 

+  *  +  »  +     +  />_ 

A -A 

The  bending  moments  at  these  points  are  readily  found 
by  taking  the  moments  of  the  external  forces  on  one  side  of 
the  point  in  question ;  thus  M  at  the  first  point  (remember- 
Wl 

ing  that  M=  for  a  uniformly  loaded  cantilever)  is 

2 

M  =  Ml.  P(**-m)\ 

2  2  ' 


Mi  =  Pb  +  pt{b  +  c)  -  (P  +  Pff ; 

Mb=^-  P(xb  -b)-Px{xh-b-c) 


pjjx6  —  m  —  a  —  n  —  a,  —  qY 

2 

In  general  cases  7J/2  and  MA  will  be  small  except  where 


FO  UNDA  TIONS.  1 89 

the  columns  are  very  far  apart,  and  the  maximum  bending 
moment  will  be  at  either  MX,M3,  or  Mb ,  according  to  which 
column  is  the  heaviest.  If  the  cast  bases  are  strong  enough 
to  carry  the  superimposed  loads  on  their  perimeters,  and 
the  long  beams  form  the  top  course,  the  values  of  M1}  M%, 
and  Mb  will  be  reduced.  M2  and  MK  would  not,  however, 
be  altered. 

Sufficient  deflection  could  hardly  take  place  to  in- 
crease materially  the  reaction  under  the  central  column,  if 
figured  as  a  continuous  girder ;  but  if  so  calculated,  the 
clay  reaction  would  be  of  a  varying  intensity,  as  in  Fig.  118. 

JWp  Jff0 


t  1  j  I  1  f  M  f  1  I  1  t  t  *  f  t  ft  |  f  ! 

 1  ■+  -I  \-lr\ 

1      7fi  7fa  7f, 

Fig.  118. 

Thus,  from  Clapyron's  formula,  we  have 

for  a  continuous  girder  of  two  equal  spans,  /.  But  in  the 
case  assumed 

k  =  =^  and  Mx  =  -  \pP  +  ^ ,  or  Mt  =  -g^-^. 

Taking  now  the  shears  St  and  5,,  on  the  left  and  right 
respectively,  of  the  reaction  Rx ,  and  remembering  that 
Sx  +  S\  =  Rx ,  we  have 


Then 


M--M0i  pi        .  „ 
5,  =  —^  —+7.    and  Sx=plx. 


ARCHITECTURAL  ENGINEERING. 


where  f^/  is  the  reaction  due  to  the  loads  on  the  two  spnas 
/,  the  same  as  in  the  regular  formula  for  two  spans,  and  pj 

i  pr 

is  the  reaction  due  to  the  cantilever  load,  while  -~-  is  the 

4  I 

effect  due  to  the  use  of  the  beam  as  a  continuous  girder. 
Also, 

These  reactions  show  a  varying  tendency  in  the  unit 
pressure  on  the  clay,  as  in  Fig.  118. 

In  the  first  example  we  made  the  assumption  that  the 
reaction  from  the  clay  was  uniform  per  foot  of  length  of 
the  footing.  According  to  the  law  of  the  continuous  girder 
this  would  not  be  true,  as  we  have  seen  ;  but  when  we  con- 
sider that  the  beams  are  generally  of  sufficient  depth  to 
prevent  any  appreciable  deflection,  and  that  the  unifying 
tendencies  of  the  concrete  cause  the  footing  to  act  more  or 
less  as  a  whole,  the  assumption  is  undoubtedly  justifiable. 

SETTLEMENT. 

It  must  not  be  forgotten  that  the  footings  are  designed 
for  the  final  loads  that  rest  on  them,  and  at  all  stages  of  the 
construction  the  same  relation  must  be  maintained  between 
the  weights  on  the  various  piers  that  will  exist  in  the  com- 
pleted state,  if  uniform  settlement  is  desired.  This  was  well 
exemplified  in  the  case  of  the  Auditorium  tower,  which 
extends  many  stories  above  the  main  building,  thus  bring- 
ing greater  weights  on  the  tower  footings.  Here  the  tower 
foundations  were  loaded  with  varying  weights  of  pig  iron  at 
the  different  stages  of  construction,  in  order  that  the  proper 
relative  excess  on  these  piers  should  be  preserved  as  in  the 
final  weight.    Even  with  all  these  precautions,  and  after 


/ 

FO  UND  A  TIONS.  1 9 1 

most  careful  tests  of  the  ground  beforehand,  this  tower  has 
settled  more  than  originally  allowed  for. 

When  a  test  load  is  applied  to  the  surface,  an  initial  set- 
tlement occurs  on  the  surface  at  a  pressure  of  i  ton  per  sq. 
ft.  Another  settlement  is  produced  under  an  increased 
weight,  which  ceases  in  a  few  hours,  and  further  settlement 
will  not  directly  occur  even  with  a  load  of  4500  lbs.  to  3 
sq.  ft.  There  is,  however,  a  further  progressive  settlement, 
owing  to  the  gradual  pressing  out  of  the  water  from  the 
clay.  Baker  says :  "  The  bearing  power  of  clayey  soils 
can  be  very  much  improved  by  drainage,  or  preventing  the 
penetration  of  the  water."  That  the  water  is  pressed  from 
the  clay  was  shown  to  be  the  case  by  careful  observations 
made  at  the  Auditorium.  Wells  were  sunk  some  24'  o" 
deep,  5'  o"  in  diameter,  and  4'  6"  from  the  foundations.  The 
borings  were  made  through  the  stratified  clay,  and  it  was 
shown  that  the  clay  became  more  and  more  compact  from 
time  to  time,  thus  proving  that  this  squeezing  process  does 
take  place.  The  settlements  were  here  carefully  watched 
for  a  number  of  years,  and  they  were  found  to  be  uniform — 
about  Ty  per  month. 

If  the  building  is  heavy,  an  immediate  settlement  of 
from  2\"  to  4"  is  noticed,  followed  by  a  gradual  progres- 
sive settlement.  The  Monadnock  Building,  200'  high, 
with  3750  lbs.  per  sq.  ft.  on  footings,  settled  5",  while  6"  was 
allowed  for.  The  Western  Banknote  Building,  eighteen 
stories  high,  built  on  quicksand  over  clay,  with  solid 
masonry  walls  and  fire-proofed,  settled  2\" .  The  Home 
Insurance  Building  settled  f "  under  two  additional  stories, 
and  "The  Fair"  Building  settled  only  1". 

PILE  FOUNDATIONS. 

It  is  this  uncertainty  of  settlement,  and  limit  to  the 
bearing  capacity  of  the  clay,  which  would  seem  to  make 


T92 


ARCHITECTURAL  ENGINEERING. 


the  pile  the  best  foundation,  if  its  use  can  be  effected  with 
consistent  economy. 

Pile  foundations  were  used  in  Chicago  for  many  years 
previous  to  the  introduction  of  the  isolated  pier  method, 
and  some  of  the  oldest  and  heaviest  buildings  are  founded 
on  them  ;  notably  the  grain  elevators  along  the  Chicago 
River,  which,  in  spite  of  their  constantly  varying  loads, 
have  so  far  maintained  their  integrity,  though  few  build- 
ings could  be  more  trying  on  any  type  of  foundations. 

Some  twenty  years  ago  the  use  of  piles  in  Chicago  was 
decried  in  consequence  of  the  very  slipshod  methods  and 
designs  used  in  the  City  Hall  building.  And  as  we  look 
back  upon  the  results  of  this  work,  it  is  hardly  surprising 
that  piles  should  have  been  viewed  with  suspicion  for 
some  time  after,  by  those,  at  least,  who  looked  no  deeper 
than  the  effect,  without  considering  the  cause.  In  this 
building  the  piles  were  driven  so  near  together  that  when 
a  new  one  was  driven  its  neighbor  was  raised  up.  The 
foundations  were  put  in  uniformly,  although  the  weight 
was  far  from  being  uniform  on  the  different  piers  ;  and  even 
by  the  time  the  floors  were  placed  a  variation  of  7^"  had 
resulted  in  the  settling. 

Another  very  good  example  of  poor  pile-driving  at 
about  the  same  time  were  the  foundations  for  the  Chicago 
water-works  tower.  The  surface  material  consisted  of  about 
17'  of  pure  lake-shore  sand,  and  a  very  heavy  hammer  was 
needed  to  drive  a  pile  even  by  measurement,  the  hammer 
rebounding  three  and  four  times.  But  the  specifications 
as  to  depth  had  to  be  complied  with,  and  the  piles  were 
hammered  and  hammered  until  the  sand  was  pierced 
through,  and  a  drop  of  11"  was  suddenly  noticed. 

After  these  and  other  failures  the  stone  and  concrete 
foundation  was  used,  until  the  introduction  of  the  "  raft " 
method,  which  was  almost  universally  approved,  and  so 


FO  UND  A  TIONS.  1 93 

extensively  used  that  the  pile  method  was  for  a  time  quite 
dispensed  with.  But  in  1889  Mr.  S.  S.  Beman  revived  the 
use  of  piles  in  the  Wisconsin  Central  Depot,  under  trying- 
circumstances.  The  building  itself  is  only  eight  stories 
high,  while  the  tower,  carried  on  piles  at  20  tons  and 
more  per  pile,  is  240  ft.  high.  There  has  been  no  ap- 
preciable unequal  settlement. 

Another  firm  advocate  of  the  pile  foundation  is  Felix 
Adler  of  the  firm  of  Adler  &  Sullivan.  The  Schiller  Theatre 
Building,  by  these  architects,  was  built  on  piles,  "  as  the 
enormous  concentrations  of  loads,  next  to  adjacent  walls, 
made  it  seem  almost  impossible  to  use  iron  and  concrete 
foundations  without  an  expense  almost  prohibitive."  So  it 
was  decided  to  use  piles,  driven  50  ft.  below  datum,  loaded 
at  55  tons  per  pile,  and  cut  off  at  datum,  with  oak  grillage 
on  top  and  a  solid  bed  of  concrete  spread  over  the  entire 
area.  Mr.  Adler,  who  is  one  of  the  best  authorities  on 
pile  foundations  in  Chicago,  states  as  follows  on  this  case  : 

"As  the  tendency  in  pile-driving  was  to  raise  the  sur- 
rounding earth,  we  watched  the  adjacent  buildings  care- 
fully. It  was  found  on  driving  the  piles  in  the  first  lot  that 
an  adjacent  building  had  settled  6  in.,  and  had  to  be  raised  on 
screws;  and  throughout  the  pile-driving  these  settlements 
were  noticed,  requiring  the  greatest  care.  Another  sur- 
prise was  that  of  the  four  surrounding  buildings  the  one 
with  the  least  efficient  foundations  was  the  only  one  not 
requiring  such  attention,  and  the  piles  were  driven  right  up 
to  the  building-line  without  movement  of  the  walls.  Un- 
der the  Borden  Block,  the  heaviest  of  the  adjoining  build- 
ings, the  movement  was  such  as  to  require  holding  up,  and 
inserting  new  foundations. 

"  Another  peculiarity,  which  seemed  to  be  a  legitimate 
outcome  of  the  pile-driving,  was  the  apparent  readjustment 
of  the  particles  of  clay  and  sand  into  the  condition  of  jelly, 


194 


ARCHITECTURAL  ENGINEERING. 


thus  destroying  the  resisting  qualities.  The  water  in  the 
soil  is  not  thoroughly  mixed,  but  occurs  in  strata  or 
pockets ;  hence  the  jar  of  the  driving  caused  the  sand,  clay, 
and  water  to  mix,  forming  a  jelly.  The  water  also  rushed 
into  the  Schiller  site  from  under  the  Borden  Block,  un- 
doubtedly explaining  some  of  the  settlements." 

These  remarks  of  Mr.  Adler  certainly  show  that  the 
work  in  question  was  not  at  all  successful  as  regards  the 
adjacent  property,  and,  indeed,  such  damage  was  done  by 
the  pile-driving  in  the  case  of  the  Schiller  Theatre  that  suit 
was  instituted  against  the  owners  of  that  building,  by  the 
owners  of  the  adjacent  Borden  Block,  as  a  result  of  damage 
sustained.  A  similar  suit  was  brought  against  the  proprie- 
tors of  the  Stock  Exchange  building,  and  the  results  of  the 
suits  now  pending  must  largely  settle  the  foundation  ques- 
tion in  Chicago.  The  outcome  is  awaited  with  much  in- 
terest by  all  of  the  architects  interested  in  high-building 
methods. 

The  new  Chicago  Library  foundations  are  perhaps  the 
most  carefully  executed  pile  foundations  in  Chicago,  being 
designed  and  executed  by  Gen.  Sooysmith.  Under  the 
walls  of  this  building  three  rows  of  piles  were  driven,  and 
the  tests  were  made  as  follows :  To  give  the  conditions  as 
they  would  be  in  the  final  structure,  three  rows  of  piles 
were  driven  in  a  trench,  and  the  middle  row  was  cut  off 
below  the  other  two,  thus  bringing  all  the  bearing  on  four 
piles  only  (two  in  each  outside  row),  but  thereby  allowing 
the  outside  rows  to  derive  the  benefit  of  the  compression  of 
the  earth  due  to  the  driving  of  the  central  row.  The  work 
was  done  by  a  Nasmyth  hammer,  weighing  4500  lbs.,  fall- 
ing 42  in.,  and  having  a  velocity  of  54  blows  per  minute. 
The  last  20  ft.  were  driven  with  an  oak  follower.  The  piles 
were  driven  at  2J  ft.  centres  to  a  depth  of  52  ft.,  27  ft.  into 
soft  clay,  23  ft.  into  hard  clay,  and  2  ft.  into  the  hard-pan. 


FO  UNDA  TIONS.  1 9  5 

Their  average  diameter  was  13  in.,  and  the  area  at  the 
small  end  80  sq.  in. 

The  bearing  power  of  the  hard-pan  was  taken  at  200 
lbs.  per  sq.  in.  Rankine's  formula  gives  about  170  lbs. 
The  extreme  average  frictional  resistance  per  sq.  in.  of  the 
sides  of  the  piles,  deduced  from  experiments  under  analo- 
gous conditions,  was  15  lbs.  per  sq.  in.  The  extreme  resist- 
ance at  the  pile  point  was  200  lbs.  X  80  =  1600  lbs.  The 
average  external  surface  of  one  pile  equalled  (52  X  12  X  41) 
=  25,000  sq.  in.  At  15  lbs.  per  sq.  in.  this  gives  375,000 
lbs.,  or  195^  tons.  Disregarding  the  point  resistance,  the 
bearing  power  of  a  pile  would  be  about  187  tons. 

Assuming  the  ultimate  crushing  strength  of  wet  Norway 
pine  not  over  1,600  lbs.  per  sq.  in.,  and  with  a  factor  of 
safety  of  3,  the  safe  load  will  be  not  over  533  lbs.  per  sq.  in. 
The  piles  were  taken  at  an  average  area  of  113  sq.  in., 
which  gives  not  over  60,230  lbs.  per  pile,  or  about  30  tons. 
This  gives  a  factor  of  3  for  crushing,  and  a  factor  of  6  for 
the  frictional  resistance  of  the  soil.  If  the  timber  were 
loaded  at  one  half  its  ultimate  strength,  45  tons  could  be 
used  per  pile. 

A  platform  to  hold  a  load  of  pig  iron  was  built  resting 
on  the  outside  rows  of  piles,  and  the  weight  was  gradually 
increased  until  at  the  end  of  eleven  days  the  mass  was  38  ft. 
high,  weighing  404,800  lbs.  on  4  piles,  or  about  5oT77  tons 
per  pile.  Levels  were  taken  at  intervals  of  two  weeks,  and 
as  no  settlement  was  observed,  30  tons  per  pile  was  consid- 
ered a  safe  load. 

Tests  were  also  made  of  drawing  piles  at  this  site,  and 
an  ordinary  pile,  driven  in  clay  to  a  depth  of  45  ft.,  gave 
45,000  lbs.  resistance. 

In  localities  where  bed-rock  itself  cannot  be  reached 
with  economy,  piles  will  undoubtedly  give  the  most  satis- 
factory results,  it  they  can  be  driven  to  bed-rock  or  hard- 


196 


ARCHITECTURAL  ENGINEERING. 


pan,  the  tops  cut  off  below  the  water-line,  and  all  this  with- 
out damage  to  surrounding  property. 

A  prominent  point  in  the  criticisms  of  Gen.  Sooysmith 
on  Chicago  high-building  methods  is  his  recommendation 
of  deep  piling  to  bed-rock,  with  the  tops  cut  off  15  ft.  below 
datum.  While  this  would  doubtless  be  a  good  thing,  it  is 
entirely  unnecessary  in  the  opinion  of  the  writer,  and  far 
too  expensive.  Some  reasons  for  this  difference  of  opinion 
are  the  following  :  A  number  of  high  buildings  supported 
on  piles  driven  to  hard-pan  only,  with  the  tops  cut  off  at 
datum,  are  proving  very  satisfactory.  Among  others  may 
be  mentioned  the  Home  Insurance  Building,  which  has 
settled  so  uniformly  that  the  greatest  variation  in  levels 
throughout  the  whole  is  but  three-fourths  of  an  inch. 
Piling  to  bed-rock  would  necessarily  be  very  expensive  in 
many  localities,  and  in  parts  of  Chicago  this  would  mean 
80  ft.  below  the  sidewalk  level ;  and  if  the  piles  were  driven 
from  a  sub  basement,  as  proposed  by  Gen.  Sooysmith,  the 
trouble  and  expense  of  draining  this  area  below  the  sewer 
level  would  be  very  great.  If  piles  are  to  be  used  at  all,  a 
proper  penetration  of  the  hard  dry  clay  would  seem  suffi- 
cient, with  the  tops  cut  off  at  datum.  The  large  grain  ele- 
vators along  the  Chicago  River,  with  their  constantly  vary- 
ing loads,  which  prove  a  most  severe  test,  have  stood  with- 
out blemish,  as  before  said. 

And  that  such  piling  is  the  only  system  of  foundations 
to  be  recommended,  as  Gen.  Sooysmith  thinks,  might  be 
questioned.  There  can  be  no  doubt  that  proper  piling,  or 
caissons  sunk  to  bed-rock,  must  be  employed  where  room 
cannot  be  had  for  steel  foundations  proportioned  at  3000 
lbs.  per  sq.  ft.  of  clay  area,  but  some  of  the  disadvantages 
of  piling  have  already  been  pointed  out.  The  general  law 
of  damage  to  adjacent  property  includes  the  driving  of 
pile  foundations,  and  the  difficulty  encountered  in  caring 


FO  UNDA  TIONS.  1 97 

lor  surrounding  buildings  must  certainly  not  be  overlooked. 
Where  all  buildings  are  built  on  piles,  the  adjacent  prop- 
erty need  not  be  injured. 

Another  objection  to  piling  next  to  buildings  supported 
on  steel  foundations  lies  in  the  difficulty  of  supporting  the 
walls  on  screws  to  allow  for  additional  settlement  during 
and  after  the  placing  of  the  new  foundations.  This  can 
always  be  done  when  new  steel  foundations  are  used,  but 
it  becomes  much  more  difficult  and  dangerous  with  the  use 
of  piles. 

The  method  of  independent  piers  and  raft  foundations 
has  certainly  proved  quite  satisfactory  in  its  very  extensive 
use  in  Chicago,  and,  with  such  uniform  settlement  as  has 
resulted,  on  account  of  the  care  that  was  taken  beforehand, 
it  answers  all  the  requirements  made  of  it.  The  writer 
has  a  preference  for  pile  foundations,  but  the  many  advan- 
tages that  attend  the  other  kind  must  be  freely  acknowl- 
edged. 

PNEUMATIC  FOUNDATIONS. 

Pneumatic  caissons  have  lately  been  employed  in  a 
notable  example  of  high  building  construction  in  New 
York  City,  namely  in  the  Manhattan  Life  Insurance  Build- 
ing. The  building  proper  is  seventeen  stories  high,  with 
a  tower  on  top,  terminating  in  a  dome.  The  main  roof  is 
at  an  elevation  of  242'  o"  from  the  widewalk,  and  from  side- 
walk to  base  of  flagstaff  =  347'  6",  and  from  base  of  foun- 
dations to  top  of  dome  =  408'  o" .  This  makes  the  dome 
61 '  o"  higher  than  the  neighboring  spire  of  "  Old  Trinity." 

The  area  of  the  lot  is,  approximately,  120'  o"  deep  X  67' 
o"  frontage,  or  8,000  square  feet,  which,  with  the  estimated 
total  weight  of  the  building  of  some  30,000  tons,  would 
give  a  load  of  7,500  lbs.  per  square  foot  of  lot  area. 

The  natural  soil  at  the  site  consisted  of  mud  and  quick- 


ARCHITECTURAL  ENGINEERING. 


sand  to  a  depth  of  some  54/  o",  down  to  bed-rock.  Had 
piles  been  used,  as  close  together  as  the  New  York  build- 
ing law  allows,  or  30"  centre  to  centre,  over  the  entire 
area,  some  1323  piles  could  have  been  driven,  with  an 
average  load  of  45,300  lbs.  each.  This  was  inadmissible, 
as  the  building  law  limits  the  load  per  pile  to  40,000  lbs. 
each,  when  driven  2'  6"  centres. 

A  new  departure  in  foundations  was  therefore  neces- 
sary, especially  as  the  surrounding  buildings  were  built  on 
the  natural  earth,  making  them  particularly  liable  to  in- 
jury in  case  of  any  increase  of  pressure  on  the  soil  from 
additional  loading,  or  decrease  in  pressure  through  deep 
excavations  or  trenches  for  piles  or  concrete  piers  below 
the  adjacent  footings. 

Pneumatic  caissons  were  thus  adopted,  the  work  being 
executed  by  Sooysmith  &  Co.  This  was  the  first  example 
of  the  pneumatic  system  as  applied  to  buildings,  although 
the  same  architects,  Kimball  &  Thompson,  had  before  used 
smaller  caissons  in  the  Fifth  Avenue  Theatre  building  in 
New  York  City,  but  without  the  use  of  compressed  air. 

Fifteen  caissons,  varying  in  size  from  9/  9"  in  diameter 
to  25'  o"  square,  supported  the  thirty-four  cast-iron  columns. 
These  caissons  were  sunk  to  an  average  depth  of  about 
31'  6"  below  the  bottoms  of  the  excavations  at  the  site. 
After  the  caissons  were  sunk  to  bed-rock  the  rock  surface 
was  dressed  and  stepped  as  required,  and  the  chambers 
and  shafts  were  then  rammed  with  concrete,  composed  of 
1  part  Alsen  cement,  2  parts  sand,  4  parts  broken  stone. 
The  superimposed  piers  were  built  of  hard-burned  brick 
laid  in  cement  mortar.  About  eight  days  were  required 
to  sink  each  caisson.  The  locations  of  the  several  caissons 
are  shown  in  Fig.  119. 

A  very  elaborate  system  of  cantilever  girders  was  used 
to  transfer  the  loads  on  the  columns  in  the  side  walls  to 


FOUND  A  TIONS. 


200  ARCHITECTURAL  ENGINEERING. 


proper  concentric  bearings  over  the  caisson  piers.  From 
these  bearings  the  load  was  distributed  over  the  whole 
masonry-work   by   means   of   large   steel   bolsters,  thus 


Fig.  i 20. 


diminishing  and  equalizing  the  unit-pressure.  A  cross- 
section  of  the  caissons  and  cantilever  girders  is  shown  in 
Fig.  120. 


CHAPTER  XI. 
UNIT-STRAINS— SPECIFICATIONS. 

The  question  of  unit-strains  will  naturally  vary  to  a  con- 
siderable extent  with  the  personal  opinions  of  the  designer 
— the  more  conservative  his  views  the  lower  his  allowances. 
But,  whatever  the  preferences  of  the  engineer  or  architect, 
he  is,  to  a  large  measure,  limited  by  the  city  building  laws 
with  which  he  is  required  to  conform.  A  comparison  be- 
tween the  building  ordinances  of  New  York,  Chicago,  and 
Boston,  given  in  the  next  chapter,  will  show  the  wide  diver- 
gence which  exists  in  their  respective  requirements. 

A  few  unit-strains  will  here  be  mentioned  as  having  been 
employed  in  Chicago  skeleton  buildings  before  the  adoption 
of  the  present  ordinance.  Cast  iron  and  timber  will  not  be 
considered  as  entering  into  modern  high-building  construc- 
tion. 

BRICKWORK. 

The  allowable  pressure  per  square  foot  on  brick  masonry 
as  used  in  the  highest  masonry  piers  in  Chicago,  namely,  in 
the  Masonic  Temple,  has  been  mentioned  before  as  12  tons. 

Prof.  I.  O.  Baker,  in  his  "  Treatise  on  Masonry  Construc- 
tion," gives  the  following  allowable  strains  on  brickwork  as 
the  practice  of  the  leading  Chicago  architects : 
10  tons  per  sq.  ft.  on  best  brickwork  laid  in  1  to  2  Portland 

cement  mortar ; 
&  tons  per  sq.  ft.  for  good  brick  laid  in  1  to  2  Rosendale 
cement  mortar ; 

$  tons  per  sq.  ft.  for  ordinary  brick,  laid  in  lime  mortar. 

201 


202 


ARCHITECTURAL  ENGINEERING. 


He  shows,  however,  that  these  figures  are  very  conserva- 
tive, as  his  tables  of  the  ultimate  strength  of  best  brickwork 
give  from  no  tons  with  lime  mortar  to  180  tons  with  Port- 
land cement  mortar  per  square  foot.  So  while  the  12  tons 
in  the  Masonic  Temple  was  even  greater  than  ordinary 
Chicago  practice,  Prof.  Baker  adds  that  "  reasonably  good 
brick  laid  in  lime  mortar  should  be  safe  under  a  pressure  of 
20  tons  per  sq.  ft." 

COLUMNS. 

We  have  few  experiments  of  value  on  the  ultimate 
strength  of  full-sized  columns  of  the  type  most  used  at 
present.  Building  operations  have  to  be  conducted  too 
quickly  to  allow  many  tests  on  the  full-sized  columns  before 
using.  Tests  have  been  made  on  the  full-sized  Gray  columns, 
and  on  the  Larimer  column,  as  before  referred  to.  The  only 
full-sized  tests  on  Z-bar  columns  were  made  by  C.  L.  Strobel, 
then  Chief  Engineer  of  the  Keystone  Bridge  Company  (see 
Transactions  of  the  American  Society  of  Engineers,  April, 
1888),  who  introduced  this  shape  into  the  United  States. 
But  even  these  tests  are  hardly  fair  ones  for  present  com- 
parisons, as  lattice  bars  were  used  instead  of  web  plates,  and 
almost  all  the  tests  were  for  a  much  higher  ratio  of  the 
radius  of  gyration  to  the  length  of  column  than  is  ordinarily 
met  with  in  building  work.  It  seems  as  though  higher 
breaking  loads  would  be  obtained  for  the  majority  of 
columns  as  used  at  the  present  time.  Burr,  in  his  "  Strength 
and  Resistance  of  Materials,"  deduces  formulae  for  the  Key- 
stone and  Phoenix  columns,  but  none  for  the  Z  column  or 
the  box  column  of  plates  and  angles.  The  latter  type  was 
used  in  the  Masonic  Temple  in  two-story  lengths,  lattice  bars 
being  used  instead  of  the  plates  in  the  lighter  columns.  But 
as  the  height  of  a  single  story  was  less  than  12'  o"  unsupported 
length,  a  uniform  unit-strain  of  12,500  lbs.  per  sq.  in.  was 


UNIT-STRAINS— SPECIFIC  A  TIONS.  203 

used  without  reduction  by  the  radius  of  gyration,  for  alL 
concentric  loading.  Columns  with  eccentric  loads  were 
figured  for  a  unit-strain  of  12,500  lbs.  per  sq.  in.  reduced  by 
Rankine's  formula  for  eccentric  loading. 

In  the  Venetian  Building  the  columns  without  strains 
from  wind  bracing  were  figured  at  15,000  lbs.  per  sq.  in.  for 
all  concentric  dead  and  live  loads,  with  an  extra  allowance 
for  eccentric  loads.  The  columns  carrying  strains  from  the 
wind  bracing  were  figured  at  20,000  lbs.  per  sq.  in.  for  all 
concentric  loads, — dead,  live,  and  wind, — with  an  additional 
allowance  for  eccentric  loading.  In  these  columns  the  wind- 
strains  amounted  to  from  35  to  40  per  cent  of  the  total  load, 
so  that  this  mode  of  treatment  of  using  a  higher  unit-strain 
gave  a  much  greater  section  to  the  column  than  if  a  lower 
unit-strain  had  been  used  and  the  wind  forces  disregarded. 
These  unit-strains  have  been  used  in  a  number  of  Chicago 
high  buildings,  notwithstanding  some  rather  severe  criti- 
cism. 

In  "The  Fair"  Building,  by  W.  L.  B.  Jenney,  architect, 
12,000  lbs.  was  used  uniformly  on  all  columns,  with  no  allow- 
ance for  eccentric  loading.  This  building  is  one  of  the 
heaviest  in  the  city  of  Chicago,  being  figured  for  130  lbs.  live 
load  per  square  foot  for  the  1st,  2d,  3d,  4th,  and  6th  floors,  200 
lbs.  for  the  5th  floor,  100  lbs.  for  the  7th  and  8th  floors,  with 
the  rest  at  75  lbs.,  all  in  addition  to  dead  loads.  Great  care 
was  taken  in  providing  good  connections  throughout. 

In  the  Fort  Dearborn  Building,  by  the  same  architect,  a 
uniform  unit-strain  of  13,000  lbs.  per  sq.  in.  was  used  on  all 
columns,  made  of  channels  and  plates,  with  a  proper  reduc- 
tion for  eccentric  loading. 

The  writer  believes  that  with  the  use  of  a  mild  steel,  of 
an  ultimate  strength  of  from  65,000  to  68,000  lbs.  per  sq.  in., 
15,000  or  16,000  lbs.  per  sq.  in.  may  safely  be  used  for  all 
concentric  dead,  live,  and  wind  loads  combined  (with  an 


204 


ARCHITECTURAL  ENGINEERING. 


additional  allowance  for  eccentric  loading  as  before  de- 
scribed), provided  that  the  wind  pressure  is  taken  at  not 
less  than  30  lbs.  per  sq.  ft,  and  that  the  live  loads  on  the 
floor  systems  are  assumed  as  required  by  the  municipal 
building  laws.  With  careful  regard  for  all  connections, 
and  remembering  that  the  strength  of  a  structure  lies  in  its 
weakest  point,  these  unit-strains  would  seem  to  satisfy  both 
the  conditions  of  proper  economy  and  satisfactory  design. 

The  use  of  20,000  lbs.  per  sq.  in.,  as  in  the  Venetian 
Building,  would  seem  too  high,  especially  when  the  live  load 
is  but  35  lbs.  per  sq.  ft.  on  the  floor  systems,  and  when  but 
50  per  cent  of  this  is  considered  as  transferred  to  the 
columns. 

SPECIFICATIONS  FOR  STRUCTURAL  STEELWORK. 

Material  and  Workmanship. — The  entire  structural  frame- 
work, as  indicated  by  the  framing  plans,  or  as  specified,  is  to 
be  of  wrought  steel,  of  quality  hereinafter  designated,  all 
material  to  be  provided  and  put  in  place  by  this  contractor 
unless  specifically  stated  to  the  contrary.  All  work  to  be 
done  in  a  neat  and  skilful  manner,  as  per  detail  or  specified, 
and  if  not  detailed  or  specified,  as  directed  by  the  superin- 
tendent to  his  entire  satisfaction. 

Quality  and  Material. — Steel  may  be  made  by  either  the 
Bessemer  or  open  hearth  process.  It  shall  be  uniform  in 
quality,  and  must  not  in  any  case  contain  over  0.10  of  1  per 
cent  of  phosphorus. 

The  grade  of  steel  used  (except  for  rivets)  shall  fill  the 
following  requirements  when  tested  in  small  specimens: 

Ultimate  tensile  strength  :  60,000  to  68,000  lbs.  per  sq.  in. 
Elastic  limit :  Not  less  than  one  half  the  ultimate  strength. 
Elongation  :  Not  less  than  20  per  cent  in  8  in. 
Reduction  in  area  :  Not  less  than  40  per  cent  at  point  of 
fracture. 


/ 


UNIT-STRAINS— SPECIFIC  A  TIONS.  205 

Bending  Test. — Duplicate  specimens  will  be  required  to 
stand  bending  1800  around  a  mandrel,  the  diameter  of  which 
is  equal  to  one  and  a  half  times  the  thickness  of  the  specimen, 
without  showing  signs  of  rupture  on  either  concave  or  con- 
vex side.  After  being  heated  to  a  dark  cherry  red,  and 
quenched  in  water  at  1800  Fahr.,  the  specimen  must  stand 
bending  as  before. 

Inspection. — All  steelwork  is  to  be  inspected  from  the 
melt  to  final  delivery  of  finished  material  on  board  cars. 
The  inspection  will  include  surface,  mill,  and  shop  inspec- 
tion by  an  inspector  satisfactory  to  the  engineer,  to  whom 
all  reports  are  to  be  made.  No  work  shall  be  delivered 
until  approved  and  stamped  by  the  inspector.  All  inspec- 
tion shall  be  at  the  expense  of  this  contractor. 

Tests. — A  test  from  the  finished  material  will  be  required 
representing  each  blow  or  cast.  In  case  the  blows  or  casts 
from  which  the  blooms,  slabs,  or  billets  in  any  reheating 
furnace  charge  are  taken,  have  been  tested,  a  test  represent- 
ing the  furnace  heat  will  be  required,  and  must  conform  to 
the  requirements  as  before  specified. 

The  original  blow  or  cast  number  must  be  stamped  on 
each  ingot  from  said  blow  or  cast,  and  this  same  number, 
together  with  the  furnace  heat  number,  must  be  stamped  on 
each  piece  of  the  finished  material  from  said  blow,  cast,  or 
furnace  heat. 

Rivet  Steel. — The  steel  used  for  rivets  shall  fulfil  the  fol- 
lowing requirements: 

Ultimate  tensile  strength  :  56,000  to  62,000  lbs.  per  sq.  in. 
Elastic  limit :  Not  less  than  30,000  lbs.  per  sq.  in. 
Elongation  :  Not  less  than  25  per  cent  in  8  in. 
Reduction  of  area  at  point  of  fracture  shall  be  at  least 
50  per  cent. 

Specimens  from  the  original  bar  must  stand  bending 
1800  and  close  down  on  themselves  without  sign  of  fracture 


206 


ARCHITECTURAL  ENGINEERING. 


on  convex  side  of  curve.  Specimens  must  stand  cold 
hammering  to  one  third  the  original  thickness  without  flay- 
ing or  cracking,  and  must  stand  quenching  as  heretofore 
required  for  rolled  specimens. 

Cast  Iron. — All  cast  iron  shall  be  of  the  best  quality  of 
metal  for  the  purpose  intended.  Castings  shall  be  clean  and 
free  from  defects  of  every  kind,  and  boldly  filleted  at  all 
angles. 

The  cast  iron  must  stand  the  following  test: 

A  bar  i"  square,  $'  o"  long,  4'  6"  between  bearings,  shall 
support  a  centre  load  of  550  lbs.  without  sign  of  fracture. 

Drazvings. — All  copies  of  architects'  drawings,  shop  draw- 
ings, templates,  patterns,  models,  etc.,  and  all  necessary 
measurements  at  the  building,  shall  be  made  by  this  con- 
tractor at  his  own  expense.  All  shop  drawings  must  be 
submitted  for  the  approval  of  the  architects,  and  such 
changes  or  additions  shall  be  made  as  are  required  by  said 
architects  or  their  agent. 

Painting. — No  material  shall  be  painted  until  approved 
by  the  inspector,  nor  shall  any  painting  be  done  when 
material  is  exposed  to  rain,  or  in  otherwise  improper  con- 
dition. No  material  shall  be  shipped  until  the  paint  is 
thoroughly  dry. 

All  iron  and  steel  shall  receive  one  coat  of  best  red  lead 
ground  in  linseed-oil  before  leaving  the  shop.  When  the 
framework  is  completed,  all  exposed  portions  are  to  be 
touched  up  with  paint  as  specified,  and  the  whole  shall  then 
receive  a  second  coat  of  best  red  lead  mixed  with  linseed- 
oil. 

Beams. — All  floor,  roof,  and  other  beams  shown  on  fram- 
ing plans  to  be  of  size  and  weight  shown,  and  accurately 
located  according  to  plan.  Where  two  or  more  beams  are 
shown  side  by  side,  they  shall  be  provided  with  cast  separa- 
tors at  least  every  8'o"  apart,  but  with  never  less  than  three 


UNIT-STRAINS— SPECIFIC  A  TIONS.  20J 

in  each  span.  Each  separator  to  be  at  least  f "  thick,  and  cast 
to  fit  the  profile  of  the  beam  exactly.  Separators  must  be 
provided  at  each  and  every  bearing.  Where  the  distance 
centre  to  centre  of  beams  is  not  given  in  the  drawings,  they 
shall  be  set  at  the  minimum  distance  given  in  Carnegie's 
table  of  separators. 

Girders. — All  plate  and  lattice  girders  to  be  proportioned 
to  the  following  stresses  per  square  inch  : 

Extreme  fibre  stress          12,000  lbs. 

Compression   10,000  " 

Tension   12,000  " 

Shearing   6,000   "  for  webs,  9,000  for  rivets. 

Direct  bearing,  including  rivets,  15,000  lbs. 

In  all  built  girders  the  flanges  alone  are  to  be  considered 
as  resisting  the  bending  moments.  Both  flanges  to  be  of  the 
same  section,  the  net  section  to  be  figured  in  all  cases.  No 
angles  to  be  used  smaller  than  2\"  X  2\"  X  TV'>  and  no  webs 
to  be  of  a  thickness  less  than  f " .  Wherever  the  distance 
between  the  flange-angles  is  greater  than  70  times  the  thick- 
ness of  the  web,  stiffening  angles  shall  be  used  not  farther 
apart  than  the  total  depth  of  the  girder.  StifTeners  must  be 
provided  at  all  bearings  and  at  points  of  concentrated  load- 
ing. All  stiffeners  to  be  placed  over  filler  plates,  and  ends 
of  stiffeners,  top  and  bottom,  to  fit  closely  against  the  flange- 
angles. 

Columns. — The  maximum  strain  upon  the  metal  in  col- 
umns shall  not  exceed  12,000  lbs.  per  sq.  in.  for  a  length  less 
than  or  equal  to  90  radii  of  gyration.  For  columns  of  a 
greater  length  the   metal  shall  be  proportioned  by  the 

formula  17,000  —        /  to  be  taken  in  inches.    No  column 
'  r 

to  have  an  unsupported  length  of  more  than  30  times  its 
least  lateral  dimension.  The  least  radius  of  gyration  shall 
be  used. 


208 


ARCHITECTURAL  ENGINEERING. 


All  columns,  where  possible,  shall  be  made  in  two-story 
lengths,  breaking  joints  alternately.  Columns  to  be  built 
with  vertical  connection-plates  or  splice-plates,  all  joints  to 
be  equal  in  strength  to  the  column  itself.  Bearing-surfaces 
must  be  "  finished  "  and  protected  by  white  lead  and  tallow. 
All  columns  must  be  perfectly  true  and  tested  at  frequent 
intervals.    "  Shimming"  will  not  be  allowed. 

Castings. — Cast  iron  used  in  the  shape  of  lintels,  corbels, 
or  brackets  shall  be  so  proportioned  that  the  compressive 
strain  does  not  exceed  13,500  lbs.  per  sq.  in.,  nor  the  tensile 
strain  exceed  3,000  lbs.  per  sq.  in.  Cast-iron  plates  may  be 
loaded  to  15,000  lbs.  persq.  in.  Cast-iron  column  bases  may 
be  strained  to  6,000  lbs.  fibre  strain.  They  shall  not  give  a 
pressure  of  more  than  15  tons  per  sq.  ft.  on  brickwork,  nor 
more  than  30  tons  per  sq.  ft.  on  granite. 

Plates. — Cast-iron  plates  shall  be  set  under  ends  of  all 
beams  and  girders,  resting  on  masonry,  so  proportioned  as 
not  to  exceed  a  load  of  15  tons  per  sq.  ft.  on  brickwork,  nor 
more  than  30  tons  per  sq.  ft.  on  stone. 

Connections — Splices. — All  field-connections  and  splices  to 
be  riveted  with  hot  rivets.  Where  girders  or  beams  rest 
on  brackets  attached  to  the  columns,  such  beams  or  girders 
shall  be  riveted  through  the  bottom  flanges  to  the  bracket, 
and  also  have  connection-angles  connecting  the  top  flanges 
to  the  column.  The  ends  of  all  girders  or  beams  resting  on 
masonry  walls  or  piers  to  have  anchors  securely  embedded 
in  the  masonry-work. 

Rivets. — All  rivets  to  be  of  mild  steel,  as  before  specified. 
The  pitch  of  rivets  shall  never  be  less  than  ij"  nor  more 
than  6",  while  the  minimum  distance  from  the  centre  of  any 
rivet  to  the  edge  of  material  shall  be  ij".  No  rivets  to  be 
used  in  tension.  An  excess  of  25  per  cent  shall  be  allowed 
in  proportioning  field-rivets.  Rivet-holes  may  be  punched 
or  drilled,  but  must  not  be  more  than  I*g-"  larger  than 


I 


UNIT-STRAINS— SPECIFICA  TIONS.  20g 

diameter  of  rivet.  Rivet-holes  must  be  accurately  spaced, 
as  drift-pins  will  be  allowed  for  assembling  only.  The  rivets 
shall  completely  fill  the  holes,  with  full  heads  concentric 
with  the  rivets,  and  in  full  contact  with  the  surface  of  the 
material. 

SPECIFICATIONS  FOR  BRICKWORK,  ETC. 

(Extracts  from  Masonry  Specifications  for  the  Fort  Dearborn  Building.  Jenney 
&  Mundie,  Architects.) 

This  contractor  will  furnish  and  set  all  that  part  colored 
red  on  the  drawings,  and  not  shown  or  specified  for 
pressed  brick  or  terra-cotta ;  to  be  the  best  character  of 
common  brickwork,  laid  up  with  the  best  merchantable, 
good,  sound,  hard  bricks,  acceptable  to  the  architects,  to 
lines  and  levels  on  all  sides,  in  lime  mortar,  all  joints  being 
carefully  filled  and  the  bricks  rubbed  weli  into  place  and 
pounded  down  to  make  a  small  solid  joint.  When  laid  in 
dry,  warm  weather,  bricks  will  be  laid  wet.  The  joints  of 
all  outside  common  brick,  and  of  all  interior  brickwork  not 
to  be  plastered,  shall  be  neatly  struck  and  cleaned  down. 

Pressed-brick  Work. — The  contractor  will  furnish  and  set 
all  that  part  colored  red  on  the  drawings  and  marked  or 
shown  to  be  pressed-brick  work,  to  include  all  returns  into 
openings,  with  the  best  character  of  pressed-brick  facing  of 
even  color  and  of  the  kind  and  character  hereinafter  speci- 
fied. All  exposed  brickwork  of  areas  and  entrances  in 
fronts  marked  to  be  finished  in  pressed-brick  work  shall  be 
faced  with  the  same  character  of  pressed  brick  as  used  in 
the  adjacent  parts.  All  joints  in  the  pressed-brick  work  to 
be  neatly  rodded.  All  pressed-brick  work  to  be  laid  from 
an  outside  scaffold  in  mortar  the  color  of  the  brick.  All 
courses  to  be  gauged  true.  In  laying  pressed  brick  each 
edge  and  down  the  middle  is  to  be  buttered  and  all  vertical 
joints  to  be  filled  from  front  to  back.    The  returns  of  pressed- 


210 


ARCHITECTURAL  ENGINEERING. 


brick  work  must  be  carefully  dovetailed  into  the  common 
brickwork  or  banded  by  solid  headers. 

In  the  piers  only  solid  headers  must  be  used.  A  sample 
of  pressed  brick  is  to  be  deposited  with  the  architects. 

This  contractor  will  furnish  and  set  the  terra-cotta  or 
salt>glazed  tile  copings  to  all  masonry  walls  not  covered  by 
stone  or  metal  copings.  The  copings  are  to  be  2  inches 
wider  than  the  wall  and  to  have  lapped  joints.  Copings  to 
be  set  in  Portland  cement. 

Concrete. — This  contractor  will  furnish  and  set  all  concrete 
foundations  or  concrete  filling  shown  on  the  drawings.  All. 
concrete  shall  consist  of  equal  parts  of  Portland  cement, 
mortar,  and  broken  stone.  The  size  of  broken  stone  is  to 
be  that  of  small  egg  coal.  The  mortar  is  to  be  thoroughly 
mixed,  and  the  stone  to  be  wet  before  mixing  with  mortar. 
The  concrete  to  be  cut  over  twice.  No  more  water  to  be 
used  than  is  necessary  to  moisten  every  particle  of  cement. 
All  concrete  to  be  used  immediately  after  mixing,  and  shall 
be  pounded  hard  in  place  until  the  water  stands  on  the  top 
of  the  concrete. 

Cement  Plastering. — The  outside  of  all  mason^  walls  that 
will  come  in  contact  with  the  earth  shall  be  smooth  plas- 
tered by  this  contractor  with  a  surface  coat  of  Portland 
cement  mortar  of  an  average  thickness  of  £  inch  from  the 
lower  footings  to  the  top  of  finished  grade. 

Protection. — This  contractor  will  carefully  protect  his 
work  by  all  necessary  bracing,  and  by  covering  up  all  walls 
at  night,  in  bad  weather,  and  at  all  times  when  work  is 
liable  to  be  interrupted  either  by  storms  or  cold.  He  will 
protect  all  masonry-work  from  frosts  by  covering  with 
manure  or  other  material  satisfactory  to  the  architects. 
The  top  of  all  walls  injured  by  the  weather  shall  be  taken 
down  by  this  contractor  at  his  expense  before  recommenc- 
ing work. 


UNITS TRA INS—SPECIFICA  TIONS  2 1 1 

Footings. — Concrete  footings  shall  be  enclosed  by  2-inch 
plank  curb,  said  plank  to  be  left  in  place.  All  water  is  to 
be  baled  out  of  trenches  before  the  concrete  is  put  in. 

SPECIFICATIONS  FOR  FIRE-PROOFING. 

(Extracts  from  Fire-proofing  Specifications  for  the  Fort  Dearborn  Building. 
Jenney  &  Mundie,  Architects,  Chicago.) 

The  following  specifications  include  the  fire-proofing  of 
all  the  steel  in  the  building,  the  filling  in  between  the  beams 
forming  floors,  and  the  concreting  over  the  same  to  the  top 
of  the  floor-strips,  and  the  projections  of  the  beams  below 
the  arches. 

Also  the  covering  of  all  columns,  both  those  standing 
clear  and  those  partly  incased  in  the  walls. 

Also  the  building  of  all  tile  partitions  and  the  tile  vaults. 
Also  the  building  of  the  party-walls  over  the  present  old 
brick  walls.  Also  the  tile  floor  of  the  roof  and  pent-houses 
on  the  roof. 

All  work  shall  be  laid  in  mortar  composed  of  3  parts  of 
best  fresh  lime  mortar  and  1  part  best  Louisville  cement, 
thoroughly  mixed  together  at  time  of  using.  Said  lime 
mortar  shall  be  composed  of  fresh  burned  lime  and  clean 
sharp  sand  in  proportions  best  suited  to  this  work. 

This  contractor  shall  furnish  all  material,  including  the 
mortar  for  setting  the  same,  and  will  do  all  his  own  hoisting 
and  set  all  the  work  in  a  thoroughly  substantial  and  work- 
manlike manner  to  the  satisfaction  of  the  superintendent. 

Floors. — All  floors  shall  be  supported  on  flat  arches  set 
in  between  the  beams  and  of  a  shape  that  shall  give  a  uni- 
form flat  ceiling  in  the  rooms  below. 

The  bottoms  and  projections  of  all  beams  and  girders 
shall  be  protected  by  projecting  parts  of  tile  or  by  separate 
beam  slabs.  In  laying  the  floor  arches  every  joint  shall  be 
filled  full  over  its  entire  surface,  from  top  to  bottom. 


212 


ARCHITECTURAL  ENGINEERING. 


Floor  arches,  ten  days  after  they  are  laid  and  before  they 
are  concreted,  shall  stand  a  test  of  a  roller,  15  inches  face, 
and  loaded  so  as  to  weigh  1500  pounds,  rolled  over  them  in 
any  direction. 

All  columns  shall  be  covered  with  column  tile  held  by 
metal  clamps  both  in  horizontal  and  vertical  joints.  These 
column  protections  shall  be  so  made  as  to  conform  with  the 
city  ordinance. 

Roof. — The  roof  shall  be  supported  in  the  same  way  as 
the  floors,  only  the  soffits  may  be  segmental. 

Partitions. — All  the  partitions  shown  in  the  several  plans 
are  to  be  built  including  all  cross  and  subdivision  partitions. 
All  are  to  be  of  hollow  tile  4  inches  thick  in  the  first  and 
second  stories,  and  3  inches  thick  in  all  other  stories  for 
cross-partitions.    All  hail  partitions  to  be  4  inches  thick. 

In  glazed  partitions  the  lower  parts  and  all  parts  other 
than  the  sash  and  frames  shall  be  of  tile. 

The  tiles  shall  be  set  breaking  joints,  and  be  tied  with 
metal  ties  or  clamps. 

All  vaults  shown  on  plans  above  second  story  to  be 
built  with  vestibules,  as  shown. 

Furring. — The  outside  walls  in  the  basement,  in  the  part 
for  rent,  will  be  furred  with  3-inch  tile,  so  as  to  form  a  ver- 
tical and  true  surface  for  plastering. 

All  tilework  shall  be  straight  and  true. 

All  tilework  shall  be  thoroughly  burned  and  free  from 
serious  cracks  or  checks  or  other  damages,  and  shall  be  laid 
in  a  proper  and  workmanlike  manner. 

No  centres  to  be  lowered  until  the  mortar  has  set  hard. 

All  structural  steel  on  which  the  strength  of  the  building 
depends  in  any  way,  including  wind  bracing,  shall  be  pro- 
tected by  fire-proof  covering. 

Concreting. — This  contractor  shall  fill  in  on  top  of  the  tile 
arches  with  dry  cinder  concrete,  composed  of  reasonably 


UNI  T-S I RA INS—SPE CIFICA  TIONS.  2 1 3 

clean  soft-coal  cinders,  to  be  levelled  off  at  the  top  of  the 
highest  beams  or  girders,  and  after  the  floor-strips  are  set 
to  be  filled  in  between  said  strips  with  said  dry  cinders, 
pressed  down  hard  and  leaving  a  surface  reasonably  uniform 
i  inch  below  the  tops  of  the  strips,  so  that  the  floor  can  be 
laid  without  disturbing  the  cinders. 

All  damages  to  tilework  to  be  repaired  before  the  cin- 
ders are  laid. 

Party-walls. — Above  the  present  walls  on  the  west  and 
south  sides  this  contractor  shall  furnish  and  lav  in  the  afore- 
said cement  and  lime  mortar  hard-burnt  wall  tile.  Said 
wall  to  be  composed  of  two  6-inch  tile  between  columns, 
and  elsewhere  three  thicknesses  of  4-inch  tile  clamped  to- 
gether both  in  the  length  and  across  the  wall.  The  face  of 
the  outside  tile  shall  be  guaranteed  to  stand  weather  for  five 
years,  dating  from  the  completion  of  said  wall ;  the  contrac- 
tor agreeing  to  replace  any  tile  injured  by  the  weather 
either  in  winter  or  summer  during  said  period. 

Every  joint  in  this  wall,  both  vertical  and  horizontal, 
shall  be  thoroughly  filled  over  its  entire  surface  with  the 
mortar  before  mentioned.  All  outside  joints  to  be  struck 
in  a  neat  and  workmanlike  manner. 

TERRA-COTTA  SPECIFICATIONS. 

Material. — This  contractor  shall  furnish  and  set  wherever 
called  for  on  drawings  terra-cotta  to  exactly  match  in  color 
the  sample  submitted,  all  in  strict  accordance  with  detail 
drawings.  Material  for  all  terra-cotta  to  be  carefully  selected 
clay,  left  in  perfect  condition  after  burning,  and  uniform  in 
color.  All  pieces  to  be  perfectly  straight  and  true,  and  with 
mould  of  uniform  size  where  continuous.  No  warped  or  dis- 
colored pieces  will  be  allowed.  This  contractor  to  furnish 
a  sufficient  number  of  over-pieces,  so  as  to  avoid  all  delay. 

Modelling. — All  work  shall  be  carefully  modelled  by  skilled 


214 


ARCHITECTURAL  ENGINEERING. 


workmen,  in  strict  accordance  to  detail  drawings,  and 
models  shall  be  submitted  for  architects'  approval  before 
work  is  burned.  No  work  burnt  without  such  approval 
will  be  accepted  by  the  architects  unless  perfectly  satisfac- 
tory. 

Mortar. — All  mortar  used  for  exposed  joints  in  terra- 
cotta work  shall  correspond  in  every  particular  with  mortar 
used  for  pressed-brick  work.  It  shall  be  composed  of  lime 
putty,  colored  with  "  Pecora  "  or  "  Peerless  "  mortar  stains  ; 
colors  to  be  selected  by  the  architects. 

Ornamental  Fronts,  Belt  Courses,  Bands. — This  contrac- 
tor shall  furnish  and  set  all  ornamental  terra-cotta,  belt 
courses,  and  bands,  as  shown  on  elevations  or  sections,  or 
where  otherwise  indicated,  in  strict  accordance  with  detail 
drawings.  All  terra-cotta  work  to  be  secured  to  the  iron- 
work in  the  most  approved  manner,  with  substantial  wrought- 
iron  or  copper  anchors,  and  thoroughly  bedded  in  cement 
mortar.  All  horizontal  courses  to  have  lap  joints.  All  pro- 
jecting courses  to  have  drips  formed  on  the  under  side. 

Caps  and  Jambs,  Sills. — All  caps  and  jambs  where  indi- 
cated as  terra-cotta  will  be  constructed  in  strict  accordance 
with  detail  drawings.  All  sills  and  belt  courses  to  have 
counter-sunk  cement  joints  as  directed  by  the  superintend- 
ent. All  projecting  sills  to  have  drips  formed  on  under 
side,  and  all  sills  shall  be  raggled  for  hoop  iron,  which  shall 
be  bedded  by  this  contractor  in  cement  mortar. 

Terra-cotta  Mullions. — All  ornamental  mullions  of  terra- 
cotta to  be  secured  to  metal  uprights  in  approved  manner, 
and  well  bedded  and  slushed  with  cement  mortar. 

Cornice. — This  contractor  shall  construct  cornice  in  strict 
accordance  with  detail  drawings,  with  sufficient  projection 
through  walls  and  approved  anchorage  to  the  metal-work  to 
make  same  thoroughly  secure,  this  contractor  to  furnish  all 
necessary  anchors.     Form  raggle  in  cornice  as  shown  for 


UNITS TRA INS—SPEC1FICA  TIONS.  2 1  5 

connection  of  gutter,  this  raggle  to  be  on  face  of  terra-cotta. 
Leave  openings  in  cornice  for  down-spouts  as  shown. 

Afichors. — This  contractor  shall  furnish  all  anchors,  of 
substantial  wrought  iron  or  copper,  for  the  proper  support 
and  anchoring  of  all  terra-cotta  used  in  his  work.  All 
terra-cotta  to  be  drawn  to  tight  and  accurate  joints,  to  entire 
satisfaction  of  the  superintendent.  All  terra-cotta  must  fit 
the  supporting  metal- work  exactly. 

Cutting  and  Fitting. — This  contractor  shall  do  all  cutting 
and  fitting  necessary  to  make  his  work  perfect  in  every  par- 
ticular, all  possible  cutting  and  fitting  to  be  done  at  the 
factory  before  delivery. 

Protection  of  Terra-cotta. — All  projecting  terra-cotta  shall 
be  protected  with  sound  plank  during  the  erection  of  the 
building  by  terra-cotta  contractor,  said  protection  pieces  to 
be  removed  on  cleaning  down  of  building. 

Cleaning  Down. — This  contractor  shall  carefully  clean 
down  all  terra-cotta  work  at  completion  of  building,  when 
directed  by  the  superintendent,  and  shall  carefully  point  up 
all  joints  before  leaving  work. 


CHAPTER  XII. 


BUILDING  LAWS. 

The  building  ordinances  of  the  cities  of  New  York, 
Chicago,  and  Boston  are  all  of  comparatively  recent  adop- 
tion, and  though  perhaps  no  one  of  them  may  lay  claim  to 
being  a  model  building  law,  still  one  might  expect  to 
find  much  of  the  best  practice  and  experience  in  building 
construction  incorporated  in  one  or  all  of  these  laws. 

Some  of  the  more  important  subjects  coming  under  the 
head  of  Architectural  Engineering  may  be  compared  as 
follows : 

FLOOR  LOADS. 


The  requirements  for  live  loads  per  square  foot  on  the 
floor-beams,  over  and  above  the  dead  weight  of  the  floor 
itself,  are : 


New  York. 

Chicago. 

Boston. 

4.  Stores,  warehouses,  factories, 

70 
IOO 
I20 

150 
and  upward. 

TO) 
7o  \{e) 
70) 

150  minimum. 

Posted  nonces  of 
Allowable  Load. 

70 
TOO 
ISO 

250 

Posted  notices  in 
Bidgs.  for  Me- 
chanical or  Mer- 
cantile Purposes. 

(a)  Includes  hotels  and  apartments  in  New  York. 

{b)  Includes  apartments  and  boarding  and  lodging-houses  in  Chicago. 
\c)  Called  "  places  of  public  assembly"  in  New  York. 
\d)  Includes  stables  in  Chicago. 

(e)  Allowances  may  be  made  for  reduction  in  these  loads  on  columns  and 
foundations. 

It  will  be  seen  that  these  three  laws  agree  in  a  live 
load  of  70  lbs.  per  square  foot  for  private  dwellings.  This 
is  undoubtedly  high,  40  lbs.  per  square  foot  being  about 

216 


B  UILDING  LA  WS.  2 1 7 

the  average  in  use  by  the  best  engineers  and  consulting 
architects.  This  requirement,  taken  with  the  value  given 
for  the  strength  of  wooden  beams  in  the  Boston  law,  necessi- 
tates timbers  of  far  larger  size  than  has  been  the  practice  of 
the  best  architects,  or  as  used  in  houses  which  have  been  built 
and  occupied  from  thirty  to  fifty  years.  Kidder  shows  that 
actual  loads  in  parlors  (including  piano),  dining-rooms,  etc., 
average  only  14  to  23  lbs.  per  square  foot  of  the  whole  area. 
The  excessiveness  of  the  load  of  70  lbs.  for  dwellings  would 
seem  to  be  further  indicated  by  the  use  of  the  same  load  in 
the  Chicago  laws  for  classes  2  and  3.  New  York  and  Bos- 
ton are  about  alike  for  these  two  classes;  but  if  70  lbs.  is 
sufficient  for  office  and  public  buildings,  why  require  it  for 
lighter  private  dwellings? 

In  class  4  each  city  law  requires  that  all  floors  for  ware- 
houses, etc.,  must  be  carefully  computed,  according  to  the 
intended  use,  and  the  capacity  of  such  floors  be  posted  in 
conspicuous  places  about  the  building.  The  New  York  and 
Chicago  laws  are  much  more  explicit  on  this  point  than  is 
the  Boston  law,  while  the  Chicago  ordinance  leaves  the  re- 
quired load  to  the  judgment  of  the  architect  or  engineer  with 
the  approval  of  the  Building  Commissioner.  The  minimum 
load  of  1 50  lbs.  in  the  New  York  law  is  far  too  small  in  many 
cases,  but  the  loads  for  these  types  of  buildings  are  hard  to 
classify,  and  are  best  left  to  the  care  of  competent  designers 
under  the  approval  of  the  building  departments.  Mr.  W. 
L.  B.  Jenney  had  occasion  to  estimate  the  loads  in  the  whole- 
sale warehouse  of  Marshall  Field  &  Co.  in  Chicago,  and  the 
surprisingly  low  average  of  50  lbs.  per  square  foot  was  found 
for  the  total  floor  area,  including  all  passage-ways.  The 
maximum  load  on  limited  areas  was  found  to  be  57  lbs. 

The  writer  sees  no  reason  for  changing  the  previous 
recommendations  of  live  loads,  as  given  under  a  discussion 
of  the  floor  system,  namely  : 


218 


ARCHITECTURAL  ENGINEERING. 


40  lbs.  per  square  foot  for  dwellings  ; 

80  to  90  lbs.  for  places  of  public  gatherings,  devotional, 
educational,  or  amusement ; 

40  lbs.  for  the  upper  floors  of  office  buildings ; 

80  lbs.  for  the  lower  floors  of  office  buildings  ; 
and  from  150  to  450  lbs.  for  places  of  manufacture,  storage, 
machinery,  etc. 


WROUGHT  IRON:  STRESSES  IN  POUNDS  PER  SQUARE  INCH. 


New  York. 

Chicago. 

Boston. 

Extreme  fibre  stress,  rolled  beams 
Compression    in   flanges,  built 

Direct   bearing,   including  pins 

12,000 

12,000 

9,000  rivets. 
6,000  webs. 

15,000 

II,000 
beams  or  rails  in 
foundations. 
12,000 
12,000 

10,000 
7,500  shop  rivets 
6, coo  field  rivets 
6,000  webs. 

12,000 
12,000 

10,000 

9,000 

15,000 
18,000 
27,000,000 

STEEL:  STRESSES  IN  POUNDS  PER  SQUARE  INCH. 

New  York. 

Chicago. 

Boston. 

Extreme  fibre  stress,  rolled  beams 
Compression    in    flanges,  built 

Direct   bearing,    including  pins 

15,000 

15,000 

9,000  rivets. 
7,000  webs. 

15,000 

14,000 
in  foundations. 
16,000 
16,000 

I3.500 _ 
9,000  shop  rivets 
7,500  field  rivets. 
10,000  webs. 

16,000 
15,000 

12,000 

10,000 

18,000 
22,500 
29,000,000 

As  may  be  seen  from  these  tables,  the  Boston  law  is  the 
most  comprehensive,  while  the  Chicago  ordinance  is  singu- 
larly deficient  in  unit-stresses,  and  even  somewhat  contradic- 
tory in  some  of  the  few  values  given.    Thus  under  the  head- 


/ 

BUILDING  LAWS.  2  1 9 

ing  of  plate  girders,  fibre  stresses  of  13,500  lbs.  per  square 
inch  for  steel  and  10,000  lbs.  for  wrought  iron  are  allowed, 
while  in  a  preceding  section  "all  girders,  beams,  corbels, 
brackets,  and  trusses  "  are  allowed  fibre  stresses  of  16,000  lbs. 
for  steel,  and  12,000  lbs.  for  wrought  iron.  This  latter  sec- 
tion does  not  limit  the  use  of  these  unit-stresses  to  either 
rolled  or  built  members,  thus  clashing  with  the  require- 
ments for  plate  girders.  Still  different  fibre  stresses  are 
called  for  under  the  requirements  for  rail  or  beam  founda- 
tions, 14,000  lbs.  per  square  inch  for  steel,  and  11,000  lbs.  for 
wrought  iron.    No  values  are  given  forbearing. 

The  New  York  law,  under  the  provisions  for  plate  gird- 
ers, specifies  that  "no  part  of  the  web  shall  be  estimated  as 
flange  area,  nor  more  than  J  of  that  portion  of  the  angle-iron 
ivliicJi  lies  against  the  web."  As  the  effective  depth  of  the 
girder  is  limited  to  the  distance  between  the  centres  of 
gravity  of  the  flange  areas,  this  requirement  would  seem 
quite  unnecessary.  If  the  web  be  neglected  as  affecting  the 
flange  area,  and  proper  deductions  made  for  rivet-holes,  the 
whole  angle  areas  can  very  properly  be  used. 


COLUMNS. 

The  New  York  and  Boston  laws  both  call  for  com- 
putations by  Gordon's  formula,  using  the  constants  of 
12,000  lbs.  per  square  inch  for  steel,  and  10,000  lbs.  for 
wrought-iron  columns.  No  column  is  to  have  an  unsup- 
ported length  of  more  than  30  times  its  least  lateral  dimen- 
sion, nor  to  have  metal  less  than  \"  in  thickness. 

The  Chicago  law  allows  the  use  of  the  constant  of  12,000 
lbs.  per  square  inch  for  wrought-iron  columns,  or 

S  =  i2,ooo#      f  1  +  -2  \)a,  L  and  r  all  in  inches. 

V    1  36,0007-/ 

For  steel  columns  two  formulas  are  given  : 


220 


ARCHITECTURAL  ENGINEERING. 


S  =  17,000  —  (^r)  for  columns  more  than  60  radii  in  length, 

and  5  =  13,500^  for  columns  under  60  radii  in  length  (/  and 
r  both  in  inches).  The  formula  for  columns  over  60  radii  in 
length  gives  about  13,000  lbs.  per  square  inch  for  a  column 

in  which  -  =  66. 
r 

CAST  COLUMNS. 

The  New  York  law  specifies  that  the  computations  for 
cast  columns  shall  be  made  by  the  use  of  Gordon's  formula, 
with  the  constant  of  16,000  lbs.  per  square  inch.  All  cast 
columns  to  have  a  minimum  average  thickness  of  f  with 
an  unsupported  length  of  not  more  than  20  times  their  least 
lateral  dimensions. 

The  Chicago  law  gives  formulae  for  both  round  and  rec- 
tangular cast  columns.    For  round  cast  columns  : 


S  =  io,oootf 


1  + 


6ood 


/  =  length  of  column  in  in.; 
d  —  diam.  of  columns  in  in.; 
a  =  sectional  area  col.  in  in. 


For  rectangular  cast  columns  : 

/  and  a  as  before  ;  d  =  the  side 
are  column,  or  the  least 
:ontal  dimension  of  other 
columns. 


5  =  io,oootf 


(/  and  a 
,     /2    \  of  squa 
1  +  Soody  horizon 


The  Boston  law  provides  tables  for  both  round  and 
square  cast  columns. 


STONE. 

The  use  of  Stone  for  Walls,  Facings,  Piers,  rches, 
Specified,  in  Tons  per  Square  Foot. 


etc. 


IS  THUS 


New  York. 

Chicago. 

Boston. 

1  Not 
T  specified. 

f     3^    of     the  ultimate 
|  strength    derived  from 
J  tests,  approved  by  Com- 
j  missioner  of  Buildings 
j  Dressed  stone,   laid  in 
L  Portland  cement. 

60I   First  quality, 
(dressed  beds, 
4°  /"laid    solid  in 
30  J  cement  mortar. 

Marble  and  limestone. . 

The  safe  loads  given  in  the  Boston  law  are  about  double 
those  recommended  by  Baker,  while  the  Chicago  require- 


/ 

BUILDING  LAWS.  221 

ments,  using  ^  of  the  average  ultimate  strengths  given 
by  Prof.  Baker,  allow  38  tons  on  granite,  30  tons  on  lime- 
stone, and  24  tons  on  sandstone  per  square  foot. 

The  use  of  ashlar  masonry  in  wall  facings  is  limited  as 
follows :  Boston  law  :  "  In  reckoning  the  thickness  of  walls 
ashlar  shall  not  be  included  unless  it  be  at  least  8"  thick.  In 
walls  required  to  be  16"  thick  or  over  the  full  thickness  of 
the  ashlar  shall  be  allowed;  in  walls  less  than  16"  thick,  only 
half  the  thickness  of  the  ashlar  shall  be  included.  Ashlar 
shall  be  at  least  4"  thick,  and  properly  held  by  metal  clamps 
to  the  backing,  or  properly  bonded  to  the  same." 

Chicago  law:  "Stone  may  be  used  as  facing  for  brick  walls 
under  the  following  conditions  :  If  the  facing  is  ashlar,  with- 
out bond  courses,  and  the  individual  courses  thereof  meas- 
ure in  height  between  bond  stones  more  than  six  times  the 
thickness  of  the  ashlar,  then  each  piece  of  ashlar  facing  shall 
be  united  to  the  brickwork  with  iron  anchors,  at  least  two 
to  each  piece,  and  reaching  at  least  8"  over  the  brick 
wall,  and  hooked  into  the  stone  facing  as  well  as  the  brick 
backing.  Wherever  ashlar,  as  before  described,  is  used,  it 
shall  not  be  counted  as  forming  part  of  the  bearing-surface 
of  the  wall,  and  the  brick  backing  shall  be  of  the  thickness  of 
wall  herein  specified  for  the  different  kinds  of  building. 

"  If  stone  facing  is  used  with  bond  courses  at  a  distance 
apart  of  not  more  than  six  times  the  thickness  of  the  ashlar, 
and  where  the  width  of  bearing  of  the  bond  courses  upon 
the  backing  of  such  ashlar  is  at  least  twice  the  thickness  of 
the  ashlar,  and  in  no  case  less  than  8",  then  such  ashlar 
facing  shall  be  counted  as  forming  part  of  the  wall, 
and  the  total  thickness  of  wall  and  facing  shall  not  be  re- 
quired to  be  more  than  herein  specified  for  walls  of  the 
different  classes  of  buildings." 

New  York  law  :  "  All  stone  used  for  the  facing  of  any 
building,  and  known  as  ashlar,  shall  not  be  less  than  4"  thick. 


222 


ARCHITECTURAL  ENGINEERING. 


Stone  ashlar  shall  be  anchored  to  the  backing,  and  the  back- 
ing shall  be  of  such  thickness  as  to  make  the  walls  (inde- 
pendent of  the  ashlar)  conform,  as  to  the  thickness,  with  the 
requirements  of  this  ordinance." 

Dimension  stones,  as  specified  in  the  Chicago  ordinance 
for  foundations,  shall  not  be  subjected  to  a  load  of  more 
than  10  tons  per  square  foot.  If  the  beds  of  the  stones  are 
dressed  and  levelled  off  to  uniform  surface,  and  the  stones  are 
set  in  Portland  cement  mortar,  this  load  may  be  increased 
to  25  tons  per  square  foot. 


BRICKWORK:  ALLOWABLE  PRESSURES  IN  TONS  PER  SQUARE 

FOOT. 


New  York. 

Chicago. 

Boston. 

Brickwork  laid  in  cement 

1 

iiiUa) 

8  J 

15  tons  with  Port-"] 
land  cement.  ! 

12  tons  with  or- 
dinary  cement,  f  ^  ' 

8  tons  with  lime  j 
mortar.  J 

I51 

12  K<r) 
SJ 

Brickwork  laid  in  cement 

and  lime  mortar  

Brickwork   laid    in  lime 

(a)  Isolated  brick  piers  shall  not  exceed  12  times  their  least  dimensions. 

(b)  The  loads  permitted  for  brick  piers  shall  be  25  per  cent  less  than  in 
walls. 

In  walls  an  additional  25  per  cent  may  be  allowed  if  brickwork  is  thor- 
oughly grouted  or  "  shoved." 

A  further  20  per  cent  additional  allowance  may  be  made  if  walls  are  built 
of  sewer  brick  only,  or,  if  vitrified  paving  bricks  are  used,  this  allowance  may 
be  made  30  per  cent. 

(c)  In  brick  piers  in  which  the  height  is  from  6  to  12  times  the  least  dimen- 
sion, these  pressures  are  reduced  to  13,  10,  and  7  tons  respectively  for  the 
mortars  as  above  given. 


BEARING  POWER  OF  PILES  AND  SOILS. 
Given  in  Pounds  per  Pile,  or  per  Square  Foot  on  Footings. 


New  York. 

Chicago. 

Boston. 

40,000 

I  Not 
f  specified. 

8,000 

50,000 
4,000 
3.500 
3,000 

1 

J 

Not 
"  specified. 

Pure  clay,  at  least  15  ft.  thick.  . . 
Dry  sand,  at  least  15  ft.  thick. .  . 

"  Good  solid,  natural  earth  "... 

It  would  certainly  seem  quite  remarkable  that  a  city  of 
the  size  of  Boston  should  fail  to  specify  any  unit  loads  for 


BUILDING  LAWS.  22$ 

foundations.  For  ordinary  footings  the  only  requirements 
are  that  "  the  foundation,  with  the  superstructure  which  it 
supports,  shall  not  overload  the  material  on  which  it  rests." 
Piles  are  specified  for  use  "  where  the  nature  of  the  ground 
requires  it,"  and  "  the  number,  diameter,  and  bearing  of  such 
piles  shall  be  sufficient  to  support  the  superstructure  pro- 
posed." All  piles  must  be  capped  with  block  granite  level- 
lers, and  must  not  be  over  3'  o"  centres  in  the  direction  of 
the  wall. 

It  is  to  be  hoped  that  the  building  department  of  the 
city  of  Boston  is  less  of  a  political  organization  than  is  the 
case  in  most  large  American  cities,  or  that  the  contractors 
of  that  city  are  more  conscientious  than  the  average.  The 
New  York  laws,  in  the  requirements  for  pile  foundations, 
permit  a  5"  point,  while  no  mention  is  made  of  the  butt  end. 
Piles  are  usually  specified  with  8"  points  and  14"  butts,  and 
for  such  piles  the  allowable  pressure  of  20  tons  under  the 
New  York  law  is  certainly  very  conservative  ;  30  tons  are 
very  commonly  used  for  piles  of  6"  to  8"  point,  and  12"  to 
16"  butt. 

The  New  York  laws  also  require  that  "  if,  in  place  of  a 
continuous  foundation  wall,  isolated  piers  are  to  be  built  to 
support  the  superstructure  where  the  nature  of  the  ground 
and  the  character  of  the  building  make  it  necessary,  inverted 
arches  shall  be  turned  between  the  piers  at  least  12"  thick 
and  of  the  full  width  of  the  piers."  This  practice  has  long 
since  been  condemned  in  Chicago,  as  in  no  way  satisfactory 
or  desirable. 

The  Chicago  building  ordinance  is  certainly  far  superior 
to  those  we  have  just  mentioned,  as  regards  the  subject  of 
foundations,  and  the  following  quotations  would  seem  to 
recommend  themselves  for  general  application. 

"  Foundations  shall  be  proportioned  to  the  actual  average 


224 


ARCHITECTURAL  ENGINEERING. 


loads  they  will  have  to  carry  in  the  completed  and  occupied 
building,  and  not  to  theoretical  or  occasional  loads." 

"  Foundations  shall  be  constructed  of  either  of  the  fol- 
lowing :  Portland  cement  concrete,  or  Portland  cement  con- 
crete and  steel  or  iron,  or  dimension  stone,  or  sewer  or  pav- 
ing brick,  or  timber  piles  covered  with  grillage  of  oak  tim- 
ber, or  a  grillage  of  oak  timber  alone  ;  it  being,  however, 
provided  that  timber  shall  not  be  used  in  connection  with 
any  foundation  at  a  level  higher  than  city  datum." 

"  Where  pile  foundations  are  used,  borings  of  the  same 
shall  first  be  made  to  determine  the  position  of  the  under- 
lying stratum  of  hard  clay  or  rock,  and  the  piles  shall  be 
made  long  enough  to  reach  to  hard  clay  or  rock,  and  they 
shall  be  driven  down  to  reach  the  same,  and  such  piles  shall 
not  be  loaded  more  than  25  tons  to  each  pile.  The  heads  of 
the  piles  are  to  be  protected  against  splitting  while  they  are 
being  driven,  and  after  having  been  driven  the  piles  are  to 
be  sawed  off  to  uniform  level  and  covered  with  an  oak  tim- 
ber grillage,  so  proportioned  that  in  the  transmission  of 
strains  from  pile  to  pile  the  extreme  fibre  strain  in  the  tim- 
bers composing  the  grillage  shall  not  be  more  than  1200  lbs. 
to  the  square  inch." 

The  bearings  on  other  materials  than  piles  are  then  given, 
as  in  previous  table.  The  cement  to  be  used  in  concrete 
footings  "  shall  not  be  less  than  90  per  cent  fine  on  80-mesh 
sieve,  and  when  mixed  one  part  of  cement  to  one  part  of 
clean,  sharp  sand,  moulded  into  briquettes  of  one  square  inch 
cross-section,  shall  not  break  when  seven  days  old  at  less 
than  225  lbs.  tensile  strain,  nor  at  thirty  days  at  less  than 
275  lbs.  tensile  strain." 

In  view  of  the  many  discussions  at  the  present  day  it 
will  be  interesting  to  note  the  requirements  for  the  coating 
or  painting  of  rails  or  beams  in  foundations. 

The  Boston  law  requires  that  "all  metal  foundations  and 


I 

B UILD ING  LA  WS.  22$ 

all  constructional  ironwork  underground  shall  be  protected 
from  dampness  by  concrete,  in  addition  to  two  coats  of  red 
lead,  or  other  material  approved  by  the  inspector." 

New  York  law  :  "  When  crib  footings  of  iron  or  steel  are 
used  below  the  water-level,  the  same  shall  be  entirely  coated 
with  coal-tar,  paraffine  varnish,  or  other  suitable  preparation 
before  being  placed  in  position.  When  footings  of  iron  or 
steel  for  columns  are  placed  below  the  water-level,  they 
shall  be  similarly  coated  for  preservation  against  rust." 

The  Chicago  ordinance  requires  a  perfect  covering  of 
concrete  only  :  "  If  steel  or  iron  rails  or  beams  are  used  as 
parts  of  foundations,  they  must  be  thoroughly  embedded  in 
a  concrete,  the  ingredients  of  which  must  be  such  that  after 
proper  ramming  the  interior  of  the  mass  will  be  free  from 
cavities.  The  beams  or  rails  must  be  entirely  enveloped  in 
concrete,  and  around  the  exposed  external  surfaces  of  such 
concrete  foundations  there  must  be  a  coating  of  Portland 
cement  mortar  not  less  than  one  inch  thick. 

WIND  PRESSURE. 

No  mention  is  made  of  the  wind  pressure  to  be  figured  in 
either  the  New  York  or  Boston  law,  except  that  the  former 
law  requires  a  live  load  of  50  lbs.  per  square  foot  to  be  taken 
for  all  roofs. 

The  Chicago  law  provides  as  follows:  "  In  the  case  of 
all  buildings  the  height  of  which  is  more  than  1 J  times  their 
least  horizontal  dimension,  allowances  shall  be  made  for 
wind  pressure,  which  shall  not  be  figured  at  less  than  30  lbs. 
for  each  square  foot  of  exposed  surface.  The  precautions 
against  the  effects  of  wind  pressure  may  take  the  form  of 
any  one  or  all  of  the  following  factors  of  resistance  to 
wind  pressure  : 

"  First.  Dead  weight  of  structure,  especially  in  its  lower 
parts. 


226 


ARCHITECTURAL  ENGINEERING. 


"  Second.  Diagonal  braces. 

"  Third.  Rigidity  of  connections  between  vertical  and 
horizontal  members. 

"  Fourth.  By  constructing  iron  or  steel  pillars  in  such 
manner  as  to  pass  through  two  stories  with  joints  breaking 
in  alternate  stories." 

ALLOWABLE  HEIGHT  OF  BUILDINGS. 

The  New  York  law  sets  no  limitation  on  the  height  of 
buildings  in  that  city. 

Boston  law :  "  No  building  or  other  structure  hereafter 
erected,  except  a  church  spire,  shall  be  of  a  height  exceed- 
ing 2\  times  the  width  of  the  widest  street  on  which  the 
building  or  structure  stands,  whether  such  street  is  a 
public  street  or  place  or  a  private  way  existing  at  the 
passage  of  this  act  or  thereafter  approved  as  provided  by 
law,  nor  exceeding  125  feet  in  any  case;  such  width  to 
be  the  width  from  the  face  of  the  building  or  structure  to 
the  line  of  the  street  on  the  other  side,  or  if  the  street  is 
of  uneven  width,  such  width  to  be  the  average  width  of 
the  part  of  the  street  opposite  the  building  or  struc- 
ture." 

Chicago  ordinance  :  "  No  building  shall  be  erected  in  the 
city  of  Chicago  of  greater  height  than  160  feet  from  the 
sidewalk  level  to  the  highest  point  of  external  bearing, 
walls.  And  the  height  of  no  building  of  skeleton  construc- 
tion shall  be  more  than  three  times  its  least  horizontal 
dimension.  And  no  building  of  masonry  construction  shall 
be  more  than  four  times  as  high  as  its  least  horizontal 
dimension." 

The  buildings  which  have  been  termed  "  sky-scrapers  " 
in  Chicago  were  all  built  before  the  passage  of  this  ordi- 
nance, or  on  building  permits  which  were  issued  before  the 
law  went  into  effect. 


APPENDIX  TABLE. 


227 


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228 


A R CHI TECT URA L  ENGINEER ING. 


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£  33 


INDEX. 


PAGE 

Anchors  for  terra  cotta  work   104 

specifications  for     215 

Ashland  Block,  data  about   228 

wind-bracing  in   148 

Athletic  Club  Building,  data  about   228 

fire  in   13,  75 

fire-proofing  of  columns                                       .  20 

Auditorium,  data  about   227 

foundations  of   190 

settlement  of   191 

Auditorium  Annex,  data  about   228 

Bay  windows,  construction  of   107 

floors  and  ceilings  in   112 

framing  of,  for  Reliance  Building    109 

Masonic  Temple   109 

spandrel  sections,  Reliance  Building                                 .  .  112 

Beam  footings,  calculation  of   180 

foundations   178 

Beams  in  floor  system   82 

spandrel   100 

specifications  for   206 

Book-tile     164 

Borings  for  foundations   171 

Boston  Building  Law — allowable  height  of  buildings   226 

floor  loads   216 

foundations    222 

loads  on  brick- work   222 

loads  on  masonry   220 

strength  of  columns                                           219,  220 

wrought-iron  and  steel   218 

Box  columns  124,  126,  131 

fire-proofing  of   134 

Boyce  Building,  data  about   228 

Brackets  for  bay  windows                                                            u   108 

Reliance  Building   112 

229 


230 


INDEX. 


PAGE 

Brick,  hollow,  used  for  fire-proofing   134 

Brickwork — allowable  pressure  on  201 

building  laws   220 

specifications  for   209 

Building  Laws  ,   216 

brick- work   222 

cast  columns   .  .  220 

columns   219 

foundations   222 

height  of  buildings    226 

stone,  walls,  piers,  etc   220 

wind  pressure   225 

wrought-iron  and  steel   218 

Built  sections  vs.  rolled  beams.   160 

Caissons — pneumatic ...    198 

Cantilever  girders   186,  198 

Cast  columns — building  laws   220 

disadvantages  of   114 

joints  for.   114 

Castings — specifications  for.  ,   208 

Cast-iron — specifications  for   2o(> 

Caxton  Building — data  about   227 

Ceilings — suspended   165 

Cement  plastering — specifications  for     210 

Champlain  Building — data  about   227 

floor-plan  of   39 

Chicago  Building  Law — allowable  height  of  buildings  226 

fire-proof  construction  denned   11 

fire-proofing  of  exterior  columns   95 

interior  columns   135 

floor  arches   74 

floor  loads    216 

foundations   222 

loads  on  brick-work   222 

masonry   220 

mill  construction  defined   18 

skeleton  construction  defined   94 

slow-burning  construction  defined   16 

strength  of  columns  219,  220 

wind  pressure   225 

wrought-iron  and  steel  ,   218 

Chicago  Construction    91 

Chicago  Library — pile  foundations   194 

Chicago  Office  Buildings — data  about   227,  228 

Chicago  Stock  Exchange — data  about   227 

description  of.  .  .   26 

Clearance  between  floor-beams,  girders  and  columns   85 

Columbus  Building — data  about.   228 


INDEX.  23I 

PAGE 

Column-brackets  for  bay  windows   112 

-connections   ...  127 

Pabst  Building,  Milwaukee  159 

-formula.   117 

-joints   156 

-loads,  in  Fort  Dearborn  Building   82 

-loads  in  "The  Fair"  Building   177 

-sheets   168 

Columns — building  laws   219 

capabilities  of  fire-proofing   129 

cast  vs.  wrought   113 

choice  of   131 

cost  of   119 

details  in  Venetian  Building  , . .  145 

eccentric  loading   124 

examples  of  great  length   181 

expansion  and  contraction  of   97 

fire-proofing  of   132 

Athletic  Club  Building   20 

Chicago  Law   135 

New  York  Law   96 

Gray  type   125 

joints  for  cast-iron   114 

Larimer  type     121 

limestone  pillars   131 

patent    119 

Phoenix  type  with  pintle-plates   125 

placed  in  exterior  walls   89 

plates  and  angles   124 

practical  considerations   119 

principles  of  resistance   116 

requirements  for  fire-proofing   133 

riveting  of   121 

Schiller  Theater  Building   118 

shopwork  and  workmanship   120 

specifications  for   207 

splices  in  Reliance  Building   159 

tabulation  of  loads    169 

theoretical  form   116 

two-story  lengths    158 

types  of,  for  building  work   115 

unit  strains  on   202 

used  for  pipe-space.   129 

vertical  splices   157 

Z-bar  sections  used  in  "The  Fair"  Building   130 

Y.  M.  C.  A.  Building   130 

type     123 

Combined  footings   185 


232 


INDEX. 


PAGE 

Combined  footings,  calculation  of   186 

Compression  of  clay  under  foundations   176 

Concrete  floor-arches   66,  69,  71 

in  foundations   184 

specifications  for   210 

Connection-angles — standard   85 

Connections — specifications  for   208 

Court  walls   107 

Dead  loads. ...    76 

on  floor  system  ,   80 

of  Fort  Dearborn  Building   82 

on  foundations    176 

Deflection  of  floor-beams   84 

framework,  due  to  wind   160 

Detail  plans  for  steelwork   43 

Drawings — specifications  for   206 

Earthquakes — provisions  for     156 

Eccentric  loading — calculation  of,   126 

on  columns  „   124 

Elevator  enclosures   166 

Erection  of  steel-work  ....      46 

cost  of   46 

cranes  used  in  •  46 

time  required  for  ,   46 

Field  connections   46 

Fire  loss  in  United  States   9 

Fire-proof  construction — comparative  cost  of  .   to 

definition  of   11 

Fire-proof  ducts  for  piping   21 

structures — requirements  of   16 

vaults   165 

Fire-proofing,  efficiency  of                                                                     .  131 

in  Tremont  Temple,  Boston   22 

materials  for   12 

methods  of  ^   15 

of  columns   20,  132 

of  stairways  and  elevator  shafts   19 

specifications  for   211 

Fire  test  of  fire-proof  building  ,   13 

Floor  arches,  brick   54 

Chicago  Building  Law  for   „  74 

comparative  costs  of   74 

corrugated  iron   54 

Guastavino  type   73 

hollow  tile   54 

in  Equitable  Building   56 

in  Home  Insurance  Building                                         ....  56 

in  Montauk  Building   56 


INDEX.  233 

PAGE 

Floor  arches,  Melan  system   67 

segmental   72 

steel  straps  and  concrete                                                    .  68 

test  by  fire   75 

test  of  Metropolitan  system   70 

wire  mesh   69 

Floor-beams,  calculation  of   84 

Chicago  practice   82 

connections  for   85 

deflection  of   84 

economical  arrangement  of   83 

necessary  clearance   85 

Floor-girders   86 

length  of   86 

Floor-loads   76 

Fort  Dearborn  Building     81 

Marshall  Field  Building   80 

Old  Colony  Building   81 

requirements  of  Building  Laws   216 

"  The  Fair  "  Building     177 

Floors,  specifications  for   211 

Fort  Dearborn  Building — data  about   227 

description  of    38 

floor  and  column  loads   81,  82 

unit  strains  on  columns  «   203 

wind-bracing    155 

Foundations   171 

Auditorium   190 

beam   178 

Building  Laws     222 

calculation  of  beam  footings   180 

combined  footings   186 

rail  footings   179 

Chicago  Library   194 

combined  footings   185 

concrete  in     184 

Great  Northern  Hotel   179 

independent  piers   173 

loads  on     176 

Manhattan  Building   186 

Life  Insurance  Building,  New  York   197 

Marquette  Building   184 

masonry  vs.  raft   173 

Old  Colony  Building   178 

pile   192 

pile  vs.  raft.  ...    196 

pneumatic    197 

rail   178 


234 


INDEX. 


PAGE 

Foundations,  Rand-McNally  Building   186 

Schiller  Theater  Building   103 

settlements  of   191 

"The  Fair"  Building   177 

Wisconsin  Central  Depot     193 

Framing  plans   39 

economical   83 

Furring,  specifications  for   212 

tile   165 

Girder  loads — Fort  Dearborn  Building   82 

Girders,  cantilever   186,  198 

for  floor  system   86 

spandrel   101 

specifications  for   207 

Gray  column,  details  of   125 

Great  Northern  Hotel,  data  about   228 

,  foundations  of   179 

Guastavino  floor  arches   73 

Hartford  Building,  data  about   228 

Height  of  buildings — building  laws   226 

Hollow  tile   54 

advantages  of   15 

floor  arches   56 

sustaining  power   62 

used  for  furring   165 

used  in  partitions                                     .......   163 

Home  Insurance  Building   97 

data  about   227 

settlement  of   191 

Inspection,  specifications  for    205 

Iron,  wrought,  building  laws   218 

Isabella  Building,  data  about   227 

wind-bracing   154 

Jackscrews  used  in  foundations   185 

Johnson's  patent  tile-arch   61 

Joints,  open     90 

Knee-braces,  calculation  of  ,   153 

Knee-bracing — Fort  Dearborn  Building   155 

Isabella  Building   154 

Larimer  columns — connections   121 

tests  of   123 

Lee  tile-arches   58 

Leiter  Building,  data  about   227 

Lime  vs.  cement   50 

Limestone  pillars  vs.  steel  columns   131 

Live  loads — Chicago  practice   79 

defined   76 

discussion  of,  for  office  buildings  ,   77 


I 


INDEX.  235 

PAGE 

Live  loads  on  foundations   .  176 

in  Mills  Building,  San  Francisco   79 

in  Venetian  Building   79 

Manhattan  Building,  data  about   227 

foundations  of   186 

Life  Insurance  Building,  New  York,  foundations  of   197 

Marquette  Building,  data  about   227 

description  of   26 

foundations  of   184 

Marshall  Field  Building,  data  about  ,   ...  228 

floor  loads  ,   80 

Masonic  Temple,  box  columns  in   124 

column-sheets  in   169 

data  about   228 

mechanical  plants  in   33 

piers  in   90 

special  features  in     36 

two-story  columns  in   158 

unit  strains  on  columns   202 

wind-bracing  in   143 

Masonry — building  laws   220 

piers   88 

Mechanical  features,  installation  of    21 

Melan  floor-arches   67 

Metropolitan  floor-arches   69 

Mill  construction   18 

Monadnock  Building,  data  about  ,   227,  228 

settlement  of   191 

vibrations  due  to  wind   161 

wind-bracing  in   152 

Mortar,  colored    214 

Mullions,  connections  of   101 

specifications  for   214 

Newberry  Library,  data  about   228 

New  York  Building  Laws — fire-proofing  of  columns   96 

floor  loads     216 

foundations   222 

loads  on  brick-work   222 

masonry   220 

protection  of  steel-work   53 

strength  of  columns   219,  220 

wrought-iron  and  steel   218 

New  York  Life  Insurance  Building,  data  about  227 

description  of   38 

time  required  for  erection   46 

Old  Colony  Building — column  connections   128 

data  about   227 

floor  loads   81 


236 


INDEX. 


PAGE 

Old  Colony  Building — foundations   178 

wind-bracing   152 

Owings  Building,  data  about  228 

Pabst  Building — column  connections   159 

Painting  of  metal  work,  specifications  for   206 

Panelled  beams  ,  58 

Partitions — load  per  square  feet  on  floor  system   80 

specifications  for   212 

types  of   163 

used  in  wind-bracing   136 

Permanency  of  skeleton  construction   50 

Phcenix  Building,  data  about   228 

columns,  connections  of    128 

fire-proofing  of   134 

with  pintle-plates   125 

Piers — exterior — Chicago  type   91 

Marshall  Field  Building   89 

Masonic  Temple  ,   90 

Monadnock  Building   98 

treatment  of   88 

Pile  foundations    192 

Chicago  Library   194 

tests  of   194 

Piles — building  laws    222 

Pioneer  tile-arches     58 

Plaster  used  as  fire-proofing   135 

Plates,  specifications  for,   208 

Pneumatic  caissons   198 

foundations     197 

Pontiac  Building,  data  about   227 

deflections  due  to  wind   162 

Porous  tile  in  fire-proofing  »   134 

Portal  bracing,  calculation  of   148 

Old  Colony  Building     152 

Poulson  floor-arches   72 

Pressed-brick  work,  specifications  for   209 

Rail  footings,  calculation  of   179 

foundations   178 

Rails,  properties  of    179 

Rand-McNally  Building,  data  about   228 

foundations  of   186 

Reliance  Building,  data  about   228 

description  of   26 

splices  in  columns   .  150 

wind-bracing  of   156 

Rivets,  specifications  for   208 

steel,  specifications  for   205 

Rods  for  wind-bracing   148 


INDEX.  237 

PAGE 

Roof  construction    164 

Roofs,  specifications  for   212 

Rookery  Building,  data  about   227 

Schiller  Theater  Building,  data  about   227 

foundations  of   193 

Security  Building,  data  about   228 

Segmental  floor-arches   72 

Separators   86 

Settlement,  allowance  for   172 

Chicago  Post  Office   172 

of  exterior  walls   89 

of  foundations   191 

use  of  jackscrews  in   185 

Skeleton  construction,  defined   94 

earliest  example  of  =   96 

permanency  of   50 

Skew-backs  in  tile-arches   57,  58 

Slow-burning  construction   16 

Spandrel  sections — Ashland  Block   101 

bay  windows   108 

for  Reliance  Building   112 

Fort  Dearborn  Building   101 

Marshall  Field  Building   107 

Marquette  Building   105 

Masonic  Temple,  bay  windows   109 

through  court  walls   107 

Spandrels,  defined   100 

Specifications  for  brick-work   209 

fire-proofing.   211 

structural  steel-work   204 

terra-cotta  ,   213 

Stairways   166 

Steel — requirements  of  building  laws   218 

Steel-work,  deterioration  of   50 

in  walls,  protection  of   95 

painting  of   53 

protection  of   51 

Boston  law   53 

Chicago  law   53 

New  York  law   53 

specifications  for   204 

time  required  for  erection   46 

with  cement  mortar   52 

with  lime  mortar  «   50 

Stone — building  laws   220 

Struts — wind-bracing  in  Venetian  Building   147 

Sway-rods,  calculation  of,  for  wind-pressure   140 

typical  calculation  of   143 


238  INDEX. 

PAGE 

Tacoma  Building,  data  about   227 

Terra-cotta,  anchors  for. .   104 

enamelled   16 

for  exterior  walls   91 

specifications  for    213 

used  for  column  fire-proofing    133 

Tests  of  steel-work,  specifications  for   205 

Teutonic  Building,  data  about   228 

"  The  Fair  "  Building,  data  about     227 

foundations  ,  177 

floor  loads   177 

loads  on  columns   177 

settlement  of   ,   191 

unit  strains  on  columns    203 

wind-bracing  in   144 

Tie-rods  for  floor-arches   62 

Tile-arches  for  roofs   I64 

necessary  tests  for   63 

tests  of   59 

types  most  used                            ...                              ....  6r 

weights  of   59 

Tile  floor-arches,  construction  of   56 

Tile  floors,  calculation  of   64 

Tile,  hard  vs.  porous   133 

Title  and  Trust  Building,  data  about   228 

Tremont  Temple,  Boston,  fire-proofing  in   22 

Unit  strains   201 

on  columns   202 

Unity  Building,  data  about   228 

erection  of  steel-work   46 

Vaults,  fire-proof   165 

Veneer  construction   102 

Venetian  Building,  column  sheets  in   169 

data  about   227 

floor  loads     79 

unit  strains  on  columns   203 

wind-bracing   144 

Walls,  allowable  pressure  on   201 

compression  of   89 

exterior   88 

Chicago  type   91 

thickness  of   98 

with  spandrel  girders   101 

court     107 

settlement  of  exterior  ,   89 

solid  masonry,  objections  to   88 

Western  Bank-note  Building,  settlement  of   191 

Wind-bracing — calculation  of  knee-braces   153 


/ 

INDEX.  239 

PAGE 

Wind-bracing — calculation  of  portal-bracing   148 

sway-rods   141 

Chicago  practice   137 

diversity  of  practice  in   136 

in  Ashland  Block   14S 

Fort  Dearborn  Building.     155 

Isabella  Building   154 

Masonic  Temple   143 

Monadnock  Building   152 

Old  Colony  Building   152 

Reliance  Building     156 

"  The  Fair  "  Building   144 

Venetian  Building   144 

types  of     139 

Wind-pressure — building  laws   225 

calculation  of  sway-rods   140 

experiments  on  deflection   161 

Fort  Dearborn  Building.   155 

limiting  height  of  building   160 

practical  considerations   140 

unit  loads   138 

World's  Columbian  Exposition   138 

Wisconsin  Central  Depot,  foundations  of   193 

Woman's  Temple,  data  about   228 

foundations  of   173 

World's  Columbian  Exposition — wind-pressure   138 

Y.  M.  C.  A.  Building,  data  about   227 

Z  bar  columns,  fire-proofing  of   134 

Monadnock  Building   134 

objections  to    123 

large  sections  of   130 


ARCHITECTURE. 


Building — Carpentry — Staip.s,  Etc. 


THE  ARCHITECT'S  AND  BUILDER'S  POCKET-BOOK 
KIDDER.  Of  Mensuration,  Geometry,  Trigonometry,  Rules,  Tables,  and 
Formulas  relating  to  the  strength  and  stability  of  Foundations, 
Walls,  Buttresses,  Piers,  Arches,  Posts,  Ties,  Beams,  Girders, 
Trusses,  Floors,  Roofs, etc.,  etc.  Statistics  and  Tables  Relating 
to  Carpentry,  Masonry,  Drainage,  Painting  and  Glazing, 
Plumbing,  Plastering,  Roofing,  Heating  and  Ventilation, 
Weights  of  Materials,  Capacity  and  Dimensions  of  Churches, 
Theatres,  Domes,  Towers,  Spires,  etc.,  etc.  By  F.  E.  Kidder, 
C.E.,  Consulting  Architect.  Upwards  of  600  pages  and  over 
400  plates.    Tenth  edition,  revised.    Morocco  flaps.  $4  00 

Chapter  on  Structural  Iron  rewritten,  new  chapters  on  Fire-proof  Floors 
and  Fire-proof  Construction,  Pm  and  Rivetted  Joints,  Foundations,  Bear- 
ing Power  of  Soils,  Strength  of  Masonry,  and  an  Illustrated  Glossary  of 
Technical  Terms  used  by  Architects  and  Artizans,  etc.,  etc. 

"The  hook  admirably  fulfills  its  purpose  of  becoming  an  indispensable 
companion  in  the  work  of  every  architect,  young  or  old." 

—American  Architect. 

"  We  d<>  not  hesitate  to  recommend  this  new  pocket-book."— Building. 

"I  think  there  is  no  book  that  has  done  so  much  to  give  architects  an 
intelligent  idea  of  safe  construction  as  yours  has,  and  with  the  improve- 
ments which  the  ninth  edition  contains,  I  consider  it  has  no  equal.11 

— George  F.  Hammond,  F.A.I. A.,  Architect,  Cleveland,  Ohio. 

THE  AMERICAN  HOUSE  CARPENTER. 
HATFIELD.  A  Treatise  on  the  Art  of  Building,  comprising  Styles  of  Archi- 
tecture, Strength  of  Materials,  and  the  Theory  and  Practice  of 
the  Construction  of  Floors,  Framed  Girders,  Roof  Trusses, 
Rolled  Iron  Beams,  Tubular  Iron  Girders,  Cast  Iron  Girders, 
Stairs,  Doors,  Windows,  Mouldings  and  Cornices,  together 
with  a  Compend  of  Mathematics.  A  Manual  for  the  Practical 
use  of  Architects,  Carpenters,  and  Stair  Builders.  By  R.  G. 
Hatfield.  Re-written  and  enlarged.  Numerous  fine  wood  en- 
gravings.   Twelfth  edition  8vo,  cloth,    5  00 

NOTICES  OF  FORMER  EDITIONS  OF  THE  WORK. 

"  The  clearest  and  most  thoroughly  practical  work  on  the  subject." 
"It  is  a  valuable  addition  to  the  library  of  the  architect,  and  almost 
indispensable  to  every  scientific  master-mechanic."— 11.  It.  Journal. 

THE  THEORY  OP  TRANSVERSE  STRAINS. 
HATFIELD.  And  its  Application  to  the  Construction  of  Buildings,  includ- 
ing a  full  discussion  of  the  Theory  and  Construction  of  Floor 
Beams,  Girders,  Headers,  Carriage  Beams,  Bridging,  Rolled 
Iron  Beams,  Tubular  Iron  Girders,  Cast-iron  Girders,  Framed 
Girders  and  Roof  Tresses,  with  Tables  calculated  expressly  for 
the  work,  etc.,  etc.  By  R.  G.  Hatfield,  Architect.  Fully  illus- 
trated.   Third  edition,  with  additions  8vo,  cloth,    5  00 

"The  'Theory  of  Transverse  Strains'  is  undoubtedly  the  most  important 
contribution  to  the  Science  of  Building  that  has  yet  appeared." — London, 
Architect. 

"This  work  is  a  genuine  surprise.  It  is  so  seldom  one  finds  an  architect 
who  is  thoroughly  posted  in  what  may  be  termed  the  'Engineering'  of 
Architecture,  that  we  may  well  be  pardoned  the  above  expression.  * 
We  lay  down  the  book  with  the  feeling  that  the  author  has  filled  a  gap  in 
architectural  literature,  and  done  it  well." — Engineering  News. 

STAIR-BUILDING 

MONCKTON.  In  its  various  forms  and  the  One  Plane  Method  of  Hand  Railing 
as  applied  to  drawing  Face  Moulds,  unfolding  the  center  line 
of  Wreaths,  giving  lengths  of*  Balusters  under  all  Wreaths. 
Numerous  Designs  of  Stairs,  Newels,  and  Balusters — for  the 
use  of  Architects,  Stair  Builders,  and  Carpenters.  By  James  H. 
Monckton.  Illustrated  by  81  full-page  plates  of  working 
drawings,  etc.    Third  edition  4to,  cloth  extra,    4  00 

"It  may  certainly  be  considered  the  champion  work  of  its  kind,  and  not 
only  stair  builders,  but  architects,  owe  you  a  debt  of  gratitude  for  making 
.  their  labors  lighter  in  this  regard."— O.  P.  Hatfield,  Architect. 

A  GUIDE  TO  SANITARY  HOUSE  INSPECTION; 
GERHARD.  Or,  Hints  and  Helps  regarding  the  choice  of  a  Healthful  House 

in  City  or  Country.    By  W.  P.  Gerhard,  C.E.    Third  edition. 

Square  16mo,  cloth,    1  00 
"  It  ought  to  be  in  the  hands  of  every  person  who  rents  or  hires  a  house." 

—Geo.  L.  Vose,  C.E. 


HOLLY. 


BERG. 


Preface. 
Chapter  I. 
II. 
III. 
IV. 
V. 

VI. 

VII. 
VIII. 
IX. 
X. 


BIRKMIKE. 


CAKPENTEKS'  AND  JOINERS'  HAND-BOOK. 

Containing  a  Complete  Treatise  on  Framing  Hip  and  Valley 
Roofs,  together  with  much  valuable  instruction  for  all  Me- 
chanics and  Amateurs,  useful  Rules,  Tables  never  before  pub- 
lished. By  H.  W.  Holly.  New  ed.,  with  additions.  18mo,  cloth, 

BUILDINGS  AND  STRUCTUBES    OF  AMERICAN 
RAILROADS. 

A  Reference  Book  for  Railroad  Managers,  Superintendents, 
Master  Mechanics,  Engineers,  Architects  and  Students.  By 
Walter  G.  Berg,  C.E.,  Principal  Assistant  Engineer  Lehigh 
Valley  Railroad.    4to,  cloth,  534  pag^s.    700  illustrations.  .. 

XI.   Sand  Houses. 
XII. 
XIII. 
XIV. 
XV. 
XVI. 
XVII. 
XVIII. 


$0  75 


Oil  Storage  Houses. 
Oil  Mixing  Houses. 
Water  Stations. 

Coaling  Stations  for  Locomotives. 
Engine  Houses. 
Freight  Houses. 
Platforms,  Platform  Sheds,  and 

Shelters. 
Combination  Depots. 
Flag  Depots. 
Local  Passenger  Depots. 
Terminal  Passenger  Depots. 


BIRKMIRE. 


BIRKMIRE. 


MERRILL. 


Watchman's  Shanties. 
Section  Tool  Houses. 
Section  Houses. 
Dwelling  Houses  for  Employes. 
Sleeping  Quarters,  Reading  Rooms 

and  Club  Houses  for  Employes. 
Snow  Sheds  and  Protection  Sheds 

for  Mountain  Slides. 
Signal  Towers.  XIX. 
Car  Sheds  and  Car  Cleaning  Yards.  XX. 
Ash  Pits.  XXI. 
Ice  Houses.  XXII. 

Appendix. 

ARCHITECTURAL  IRON  AND  STEEL, 

And  its  Application  in  ihe  Construction  of  Buildings.  By  Wm. 
H.  Birkmire.    Fully  illustrated  from  original  designs. 
Second  edition  8vo,  cloth, 

This  work  comprises  the  sizes  of  iron,  practical  details  and  various  tables 
for  their  use  in  Architectural  Engineering.  Is  well  recommended  by  well- 
known  Archiiectura)  Iron  Workers  and  Architects,  and  should  be  in  the 
hands  of  every  Architect,  Architectural  Student  and  Builder. 

"We  are  able  to  commend  this  work,  without  hesitation,  to  all  of  our 
readers.1'— Architecture  and  Building. 

"Architects  have  long  wanted  just  such  a  book  as  this  ;  simple,  practical 
and  comprehensive  for  daily  use  in  the  office,  by  draughtsmen  engaged  in 
layiim  out  Iron  Work."— American  Architect  and  Building  News. 

COMPOUND  RIVETED  GIRDERS  AS  APPLIED  IN 

BUILDINGS.  . 

By  Wm.  H.  Birkmire   8vo,  cloth, 

SKELETON  CONSTRUCTION  IN  BUILDINGS. 

By  Wm.  H.  Birkmire.  Fully  Illustrated  with  Engravings 
from  Practical  Examples  of  High  Buildings. 
This  work  includes  the  description  and  practical  working 
details  of  Cast-iron,  W rough t-iron,  and  Steel  Columns  in  the 
construction  of  the  skeleton  frame,  and  their  connections 
with  the  Floor  and  Curtain  Wall  Girders  ;  Stability  of  the 
Structure;  Wind  Bracing — i.  e  ,  Knee  and  Lateral  Bracing; 
Construction  of  Joints  ;  Experiments  on  the  Strength  ot  Cast- 
iron,  Wrought-iron,  and  Steel  Columns,  such  as  Z-Bar 
Columns,  Phoenix  Columns,  Plate  and  Angle  Columns,  and 
various  commercial  rolled  shape  columns;  Floor  Framing  in 
the  Skeleton  Construction;  Illustration  and  Calculation  of 
the  Columns,  Floor  Plans,  Specifications,  etc..  in  various 
high  buildings — viz.,  Havemeyer  Building,  The  New  Nether- 
lands, Home  Life  Insurance,  and  others — with  their  details 

fully  described  8vo,  cloth, 

STONES  FOR  BUILDING  AND  DECORATION. 

By  George  P.  Merrill,  Curator  of  Geology  in  the  U.  S.  National 
Museum,  Washington,  D.  C.  Treating  of  Geographical  Dis- 
tribution of  the  Minerals,  rhvsical  and  Chemical  Propetties 
of  Building  and  Decorative  Stones.  Systematic  Description 
of  Rocks,  Quarries  and  Quarry  Regions,  Methods  of  Quarrying 
and  Working,  Stone-Working  Machines  and  Implements, 
Weathering,  Selection,  Protection  and  Preservation  of  Build- 
ing Stone.  Appendices  with  Tables,  Glossary,  etc.  Illustrated 
with  eleven  full-page  plates   8vo,  cloth, 

"  It  will  fill  a  lsmg-felt  want."— Prof .  H.  S.  Williams,  Cornell  University. 

"  Entire  work  is  a  valuable  and  timely  one..'"— Engineering  News. 


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